COGNITIVE
SCIENCE
18,
123-183
(1994)
Mental Models of the Day/Night Cycle
STELLAVOSNIADOU
University of Athens, Greece
and University of Illinois at Urbana-Champaign
WILLIAMF.BREWER
University of Illinois at Urbana-Champaign
This article presents
the results of an experiment
which Investigated
elementary
school children’s
explanations
of the day/night
cycle. First, third, and fifth grade
children
were asked to explain
certain phenomena,
such as the disappearance
of
the sun during the night, the disappearance
of stars during the day, the apparent
movement
of the moon, and the alteratlon
of day and night. The results showed
that the ma/orlty
of the children
In our sample used In a consistent
fashlon
a small
number
of relatively
well-defined
mental models of the earth, the sun, and the
maon to explain
the day/night
cycle. These mental models of the day/night
cycle
were empirlcaily
accurate,
logically
consistent
and revealed
some sensltivlty
on
the part of the children
to issues of simpllclty
of explanation.
The younger
children
formed
initial mental models which provided
explanations
of the day/night
cycle
based on everyday
experience
(e.g.,
the sun goes down behind
mountains,
clouds cover up the sun). The older children
constructed
synthetic
mental models
(e.g., the sun and the moon revolve
around
the stationary
earth every 24 hours;
the earth rotates
In an up/down
direction
and the sun and maon are fixed on
opposite
sides) which represented
attempts
to synthesize
the culturally
accepted
view with aspects of their initial models.
A few of the older children
appeared
to
have constructed
a mental
model of the day/night
cycle slmllar
to the scientific
one. A theoretical
framework
is outlined
which explains
the formation
of inltial,
synthetic,
and scientific
models of the day/night
cycle in terms of the reinterpretation of a hierarchy
of constraints,
some of which are present
early in the child’s
life, and others which emerge
later out of the structure
of the acquired
knowledge.
The research reported in this article was supported in part by a grant from the National
Science Foundation, BNS-85-10254, from the Office of Educational Research and Improvement
under Cooperative Agreement No. G&)87-CIOOl-90 with the Reading Research and Education
Center and from the Cognitive Science Group, Beckman Institute, University of Illinois. This
publication does not necessarily reflect the views of the agencies supporting this research.
We wduld like to th&k the principal, teachers and children of Washington School in Urbana,
Illinois for their help in canying out this project. We also wish to thank Mar10 Schommer, Marcy
Dorfman, and Arm Jolly for their help in testing the children and scoring the data, Clark chinn
and Christos Ioannides for their comments, and Delores Plowman for secretarial work above
and beyond the call of duty.
Correspondence and requests for reprints should be sent to either Stella Vosniadou, Univexshy of Athens, 33 Ippokratus Street, Athens, Greece, or Wiiam F. Brewer, Department of
PSYchology,
University of Illinois at Urbana-Champaign, 603 B. Daniel Street, Champaign, IL
61820.
123
124
VOSNIADOU
AND
BREWER
The researchreportedin this paperinvestigateselementaryschoolchildren’s
mental representationsof the day/night cycle and attemptsto understand
how theserepresentations
changeduringthe knowledgeacquisitionprocess.
The presentwork is a continuationof earlierinvestigationsof the development of children’smentalrepresentations
of the earth(Vosniadou& Brewer,
1992),in thecontextof a largerprojectdirectedat understandingthe process
of knowledgeacquisitionin the areaof astronomy(Vosniadou& Brewer,
1987).
The Process of Acquiring Knowledge about the Physical World
During the last few yearsthere has beena surgeof researchinvestigating
how childrenacquireknowledgeaboutthe physicalworld, andmore particularly how theycometo understandthe currentlyacceptedscientificexplanationsof conceptssuchasmatter, weight,density,heat,temperature,force,
etc.This researchhasproducedagreementon at leastonefundamentalissue:
Children are not blank slateswhenthey are first exposedto the culturally
accepted,scientific views, but bring to the acquisition task some initial
knowledgeaboutthe physicalworld which appearsto be basedon interpretationsof everydayexperience.
Thereis, however,considerabledisagreement
abouthow to characterizetheseinitial knowledgestructuresand abouthow
to describetheir developmentduring the knowledgeacquisitionprocess.
Someresearchers
think that initial, intuitive, or naiveknowledgeconsists
of a largenumberof looselyorganizedphenomenologicalprincipleswhich
representminimal abstractionsof common events(e.g., disessa, 1993).
Other researchersbelievethat children start with a few, probably innate,
domain-specificprinciples, which are organizedin theory-like structures
and which constrain the knowledgeacquisition process(Gehnan, 1990;
Spelke, 1990).Researchersalso differ in whether they conceptualizethe
knowledgeacquisitionprocessin termsof the enrichmentof initial structures
(e.g., Spelke, 1991)or their replacementwith new theories(e.g., Carey,
1991).Our studiesof the developmentof the conceptof the earthhaveled
us to the developmentof a theoreticalposition (seeVosniadou,1989,in
press-a,in press-b;Vosniadou& Brewer,1992),which will be further elaboratedon in this article.
We assumethat the processof acquiringknowledgeabout the physical
world is constrainedby a few domain-specificprinciples, such as those
describedby Gehnan(1990)andSpelke(1991),whichwe callpresuppositions
(e.g., unsupportedobjects fall down). Presuppositionsmay be innate or
empirically acquiredconstraintswhich are presentfrom early infancy and
whichguidethe waychildreninterprettheir observationsandtheinformation
they receivefrom the cultureto constructknowledgestructures.We further
believethat in orderto give a full accountof the knowledgeacquisitionprocessit is necessary
to posit the existenceof a setof second-orderconstraints,
DAY/NIGHT
CYCLE
125
whichwecall beliefsandmentalmodels.Beliefsandmentalmodelsareconstraintswhich emergeout of the structureof previouslyacquiredknowledge,
andwhich in turn exerttheir influenceon the acquisitionof newknowledge.
In the context of this theoreticalframework, we arguethat conceptual
changeinvolvesmore than enrichment(e.g., Spelke,1991),and cannotbe
fully describedin termsof the directreplacementof onetheorywith another
(e.g.,Carey,1991).Conceptualchangeis seenasthe productof thegradual
lifting of constraints,as presuppositions,beliefs, and mental models are
added,eliminated,suspended,or revisedduring the knowledgeacquisition
process.
The constructof the mental model is usedhereto describethe kinds of
mentalrepresentations
wethink individualsconstructwhen.theyreasonabout
the physical world (cf. Brewer, 1987).We usethe term mental model to
denotea particular kind of mental representationwhich hasthe following
characteristics:(a) its structureis an analogto the statesof the world that it
represents(Johnson-Laird,1980,p. 90);(b) it canbe manipulatedmentally,
or “run in the mind’s eye,” to make predictionsabout the outcomesof
causalstatesin the world (Collins, 1985,p. 80);and (c) it providesexplanations of physicalphenomena(Holland, Holyoak, Nisbett, & Thagard,1986,
p. 329).We furtherassumethat mentalmodelsaredynamicstructureswhich
areusually createdon the spot to meetthe demandsof specific problemsolvingsituations(Johnson-Laird,1983;Vosniadou& Brewer,1992,p. 543).
This doesnot excludethe possibility that somemodels, or parts of them,
which havebeenprovenusefulin the past, arestoredasseparatestructures
andretrievedfrom memorywhenneeded.In additionto actingasconstraints
themselves,mental models can provide important information about the
underlying knowledgestructure (e.g., presuppositionsand beliefs) from
which they aregenerated,
Mental Models bf the Earth
In Vosniadouand Brewer(1992),we investigatedelementaryschoolchildren’s
mentalrepresentations
of the earthby askinga seriesof questionsregarding
the shapeof the earthand aboutthe regionson the earthwherepeoplelive.
We tried to understandthe mental modelsunderlyingdifferent patternsof
responsesto the samequestionsand to determinewhetherthesemodels
wereusedin a consistentfashionacrossa largenumber of problems.
The resultsof that studyshowedthat most of the childrenwe investigated
were consistentIn their use of a relatively small number of well-defined
mentalmodelsof the earth.The youngestchildrentendedto form an initial
mentalmodel of a flat earth,which could havethe shapeof a rectangleor a
disc, and which was supportedby ground. The flat earthmental model is
consistentwith everydayexperienceand is not influencedby the culturally
accepted,scientificmodel of a sphericalearth.The olderchildrentendedto
126
VOSNIADOU
AND
BREWER
form the culturally acceptedmodel of a sphericalearth, surroundedby
space,with peopleliving all aroundit (on the outside).
A numberof intermediateor syntheticmentalmodelsof the earthwere
also identified, such as the model of a dual earth, the model of a hollow
sphere,andthe modelof a flattenedsphere.Childrenwho form the synthetic
model of a dual earthbelievethat therearetwo earths-a flat one,on which
peoplelive, and a round onewhich is up in the sky. Children who hold the
hollow spheremodel believethat peoplelive on flat grounddeepinsidethe
sphericalearth,and thosethat hold the model of a flattenedspherebelieve
theearthis a sphereflat on the “top” andon the “bottom” wherepeoplelive.
Our resultsshowedthat most of the first-gradechildren, about half of
the third-gradechildren, and somewhatless than half of the fifth-grade
childrenhad formeda syntheticmentalmodelof the earth.The predominance
of syntheticmodelsof the earthdemonstrateshow difficult it is for elementary schoolchildrento form the mental representationof a sphericalearth
with peopleliving all aroundit, on the outside.This is the casedespitethe
fact that the childrenin our culture areconstantlyexposedto the scientific
information regardingthe shapeof the earth.
In order to explain the formation of thesesyntheticmental modelswe
postulatedthat children start by conceptualizingthe earth as a physical
object, ratherthan asan astronomicalobject, andthereforeassumethat all
the presuppositionswhich apply to physicalobjectsin generalapply to the
earthas well (seeVosniadou,in press-b).Two of thesepresuppositionsare
particularly important becausethey have the potential for explainingthe
syntheticmodelsthat childrenform. They are the presuppositionsthat the
groundis flat (asit appearsto be) and that unsupportedthings fall.
Syntheticmental modelsof the earth can be explainedby assumingthat
childreneitherassimilatethe culturally acceptedview of a sphericalearthto
their initial model of a flat earth,or reviseoneof thesepresuppositionsbut
not the other (Vosniadou8cBrewer,1992).For example,the syntheticmodel
of the dual earthdoesnot requirechangesin anyof the presuppositionsthat
give riseto the initial model of a flat earth. Children who form this mental
model still believethat the groundis flat and that unsupportedthings fall.
Thesechildrensimply addto their existingbeliefstheinformation that there
is anotherearthwhich is sphericaland which is up in the sky, like a planet.
The syntheticmodel of a hollow sphere,on the other hand, involvesa
modification in the child’s presuppositions.The children who form this
model havesuspendedthe presuppositionthat the earth needsto be supported,althoughthey still seemto believethat the peopleandobjectslocated
on the earthwill fall if they arenot supported.They alsocontinueto believe
that the ground is flat. In order to resolvethe conflict betweenthesepresuppositionsandthe culturally acceptedview, theycreatethe mental model
of a hollow sphere.By assumingthat the earthis a hollow sphereand that
DAY/NIGHT
CYCLE
127
peoplelive on flat groundinsidethis sphere,thesechildrensucceed
in reconcilingtheir initial presuppositions
with the scientificnotion of a sphericalearth.
From the above,we concludethat syntheticmodelsarelikely to be formed
whenthe knowledgeacquisitionprocessrequiresa revisionof presuppositionsthat arebasedon interpretationsof everydayexperience.In thesecases,
syntheticmodelsfunction asintermediatestepsin the changefrom aninitial,
intuitive model to the scientific culturally acceptedone.
The Present Study
The purposeof the presentinvestigationwasto seeif the theoreticalframework developedto accountfor the developmentof the conceptof the earth
couldexplainthe changesin elementaryschoolchildren’smentalmodelsof
the day/night cycle. In addition, we were interestedin finding out if we
could identify a small number of mental models of the day/night cycle
whichchildrenusedin a consistentmanner,andto seewhetherthesemodels
couldbecharacterizedassyntheticin wayssimilar to thosediscoveredin the
caseof the shapeof the earth.The presentstudyopensup a setof newissues
becausemental modelsof the day/night cycleinvolve not a singleconcept,
but a number of interacting concepts(earth, sun, moon, and stars),and
thesemodelsrequirethe explanationof the complexinteractionof a number
of different phenomena.
In the pagesthat follow we presenta brief accountof the explanationsof
the day/night cycle found in the history of astronomy.Wecontinuewith a
reviewof the empirical literatureon children’sexplanationsof the alternation of day and night. Then we turn to our own study.
Explanations
of the Day/Night
Cycle in the History of Astronomy
The earliesttheoriesof the day/night cyclein different culturesfocuson the
movementof the sun asthe main causeof the day/night cycle,but differ as
to whetherthey conceptualizethe sun as goingbelow the earthat night or
not. One early Chinesecosmologypostulatedthat the earth was flat and
squareandthat the sunmovedto otherdistantpartsof the earth(Needham,
1975).The earlyGreekphilosopher,Anaximenes,believedthat the earthwas
flat like a table.OneearlyGreekcommentatornotesthat Anaximenes“says
that the heavenlybodiesdo not move under the earth, as otherssuppose,
but round it, as a capturns round our head.The sunis hiddenfrom sight,
not becauseit goesunderthe earth,but becauseit is concealedby the higher
partsof the earth” (Heath, 1932,p. 10).An early Indian cosmologyalso
postulatedthat the sundid not gobelowthe earth,but insteadturneda dark
sideto earthand thenretracedits path back to the eastwhereit would rise
(Gombrich,1975).The early Greekphilosopher,Xenophanes,believedthe
earthwasflat and extendeddown indefinitely. He statedthat the sun was
128
VOSNIADOU
AND
BREWER
madeof fire. Whenthe sunset,the fire wasextinguishedandat eachdawna
new sun was ignited (Heath, 1932).
Another commonexplanationof the day/night cyclewasthat the setting
sungoesunderthe earthandbackto the placewhereit rises.The Sumerians
believedthe earth was a flat disc and that when the sun setin the west it
wentunderthe earthto risein the east(Lambert, 1975).The earlyEgyptians
believedthe earthwasthe shapeof a river valleyand that whenthe sunsetit
wentbeneaththe earthto comebackup on the otherside(Plumby, 1975).A
contemporarygroupof Quechuaspeakersin Peruhavea somewhatsimilar
view. They believethe earthto be a roughlyeast/westorientedriver valley.
They believethe sunsetsat the westend, and during thenight travelsunder
the river to comeup at the eastend (Urton, 1981).
As Greekastronomymatured,the standardview (e.g., that of Aristotle
and Ptolemy)wasthat the earthwasa spherewhich wasin the centerof the
universe.The sun and moon wereattachedto largersphereswhich rotated
aroundthemotionlessearth.The revolutionarymovementof the sunaround
the earthgaveriseto the day/night cycle(Heath, 1932).Clearlyin the early
stagesof understandingthe day/nightcycle,philosopher-scientists
developed
a wide rangeof very different modelsto accountfor observeddata. In the
nextsectionwewill examinechildren’sexplanationsof thesamephenomena.
Prior Research on Students’ Explanations
of the Day/Night
Cycle
Most studiesof knowledgeacquisitionin astronomyhave focusedon an
examinationof students’ideasaboutthe shapeof theearthandaboutgravity
(e.g., Nussbaum,1979;Nussbaum& Novak, 1976;Sneider8cPulos, 1983).
However, two relatively recentstudiesexploredstudents’explanationsof
the alternation of day and night. One study, conductedby Sadler(1987),
investigatedthe ideasof 25 ninth-gradestudentsabout the day/night cycle,
the seasons,and the phasesof the moon. This study revealedthe following
five distinct explanationsof the reasonsfor the alternationof day andnight:
(1) the earthspins,(2)the sunmovesaroundthe earth, (3)the moon blocks
out the sun,(4) the sungoesout at night, and (5)the atmosphereblocksthe
sun at night. Sadlerreportsthat overhalf of the studentswho participated
in this study werecompletinga one-yearcoursein Earth sciencesbut that
thesestudentsdid not provide correctanswersmore often than the others,
althoughthey did tend to usescientific termslike “orbit” and “tilt” more
often than the studentswho did not take the course.
A more detailedstudyof students’ideasaboutastronomicalphenomena,
including the alternationof day and night cycle,was conductedby Baxter
(1989).In this study, the responsesof 20 studentsrangingin agefrom 9 to
16 yearsof age were obtainedin individual interviews.Theseresponses
revealedthe following six explanationsof the day/night cycle: (1) the sun
goesbehindhills, (2) cloudscoverthe sun, (3)the moon coversthe sun, (4)
the sungoesaroundthe earthoncea day, (5)the earthgoesaroundthe sun
DAY/NIGHT
129
CYCLE
oncea day, and (6) the earth spins on its axis oncea day. Researchwith
additionalsubjectsshoweda preferenceon the part of the youngerstudents
for the explanationin which the earthgoesaroundthe sun oncea day and
its gradualreplacementwith theexplanationin whichtheearthspins.Despite
this change,many of the studentsage 15-16yearsstill believedthat the
reasonfor the day/night cycleis that the earthgoesaround the sun or the
sun goesaroundthe earth or that the moon coversthe sun.
While the studiesdescribedaboveidentify students’explanationsof the
day/night cycle, they are limited in their scope.The explanationsare not
describedin greatdetail, and the researchersdo not provide explicit information about the criteria usedto derive students’explanationsand about
the consistencywith which theseexplanationswere used.Neither do they
attemptto provide an accountof how theseexplanationswere formed, or
how they changewith development.We will try to answersomeof these
questionsin this paper.In the nextsectionwe will elaborateandexpandthe
theoreticalframeworkwe havedevelopedto explainthe Baxter (1989)and
Sadler(1987)findings and to make further predictions.
Constructing
a Mental Model of the Day/Night
Cycle
We assumethat the constructionof a mental model of the day/night cycle
dependson individuals’representations
of a numberof interactingconcepts
(suchasthe conceptsof the earth,the sun,andthe moon), andthat it is constrainedby two kinds of presuppositions:ontologicalpresuppositions,
such
asthepresuppositionsthat physicalobjectsaresolid, stable,fall downwhen
not supported,etc.;andep~temologicalpresuppositions, whicharepresuppositionsaboutthe generalcharacterof explanationsof physicalphenomena,
suchasa preferencefor physical/causalexplanations.Thesepresuppositions
influencethe way individualsinterprettheir observationsand the information theyreceivefrom the cultureto generatespecificbeliefsaboutthe nature
of the physicalworld and constrainthe way thesebeliefsare mappedinto
mentalmodels.An outline of this processis givenin Figure 1. Beliefs and
mental modelsthemselvescan function as second-order,domain-specific
constraintswhich further influencethe acquisitionprocess.
In the next sectionwe describethe hypothesizedknowledgeacquisition
processwhichunderlieschildren’sinitial explanationsof the day/night cycle
anddiscussthe waysin which people’smodelsof the earthand the sun further constraintheir mental modelsof the day/night phenomenon.
Hypothesized Knowledge Acquisition
Process
Presuppositions
Weassumethat elementaryschoolchildrenin our cultureoperateunderthe
constraintsof certain epistemologicalpresuppositions.For example,they
havesomecriteriawhich areusedto decidewhat constitutesa phenomenon,
Figure
Unsupported
dew,
etc.
(3)
knowledge
fall
are stable
are solid
objects
1. Hypothesized
objects
Physical
(2)
objects
Physical
(1)
Explanations
should be given
in terms of causal mechanism,
etc.
(2)
need to be explained
Phenomena
Presuppositions
(1)
I
acquisition
process
underlying
elementary
school
children’s
beliefs
sky during the day,
but not during the
The appearance
of the sun and
disappearance
of the moon and
stars a
day. The disappearance
of the sun and appearance
of the
moon and stars m
night.
1
There is ica sequence
of day and night
regarding
(5)
(3)
(4)
(2)
(1)
which explain the
and disappearance
t s appear
and disappear
the alternation
of day
and night
Something
moves in front of the
objects
and hides it
The object moves behind
something
else
The object switches
off
The object moves far away
where it cannot
be seen
The observer
turns so they
cannot see the object anymore
Mechanisms
appearance
of objects
in the sky during the
night but not during
I
DAY/NIGHT
CYCLE
131
they know that phenomenarequirean explanation,and arepredisposedto
prefercausalexplanationsof physicalphenomena.We further assumethat
children are constrainedby a set of ontologicalpresuppositionsregarding
the natureof physicalobjects(e.g, that physicalobjectsare solid, stable,
requiresupport, etc.). Thesepresuppositionsform the backgroundwithin
which children interpret their observationsand constrain the inferential
processthat usestheseobservationsto generatespecificbeliefs about the
natureof the physicalworld.
Wedo not know if thesepresuppositionsareuniversalor arerestrictedto’
childrenraisedin the culturein which thechildrenin our samplewereraised.
We havesomecross-culturaldata (Brewer,Herdrich, & Vosniadou,1987;
Samarapungavan
8cVosniadou,1988;Vosniadou& Brewer,1990)suggesting
that theontologicalpresuppositionswehaveidentifiedarefound acrossdifferentcultures,but the resolutionof this important issueremainsa question
for future research(seealso Vosniadou,in press-b).
Observations and Related Reliefs
The coreobservationrelatedto the day/night cycleis that the sunis out in
the sky during the day, but not during the night. A relatedobservationis
that the moon and starsarein the sky during the night, but not during the
day. (Most youngchildrenarenot awarethat the moon is sometimespresent
in the day sky.) From theseobservations,*and given the presuppositions
alreadydiscussed,many childrenderivethe beliefsthat day is causedby the
appearanceof the sun and the disappearance
of the moon and stars;and
that night is causedby the disappearance
of the sun and the appearanceof
the moon and stars.
The appearance
anddisappearance
of thingsis a verycommonandsalient
phenomenonin the everydayexperience
of the child. Observationsof infants
showpreoccupationwith making things appearor disappear(e.g., Piaget,
1963),and studiesof languageacquisitionshowthat words and utterances
expressingthe disappearanceand reappearanceof objects or personsare
amongthe very first to appearin the lexicon of the young child (Bloom,
1970;Brown, 1973).By the endof the preschoolyearschildrenseemto have
availableto them a numberof possiblemechanismsthat explainthe disappearanceandreappearance
of objects,suchas: somethingmovesin front of
the objectandhidesit, the objectmovesfar awaywhereit cannotbeseen,etc.
Despitethe availability of a rangeof mechanismswe predictthat the particular mechanismswhich areselectedto explainthe day/night cyclearethe
mechanismsthat meetthe constraintsimposedby children’smentalmodels
of the earthandthe sun,the moon andthe stars.Someof theseconstraints
are givenin Figure 2.
Constraints on Explanatory
Mechanisms
Explanationsof the day/night cyclemay vary dependingon how an individualconceptualizes
theearth,thesun,the moon,andthe stars.Sincemental
Figure
2. Constraints
0) Earthisrsphere,
slttmundedbyspremayormaynotmve
Mental Models of Earth
smlsItati0nary
on the
selection
(al Sunmoves
m
Mental Mod& of sun
mechanisms
that
Wa)
explain
the
IbeSungcesbehind
a-pin
d&night
Mental Models of the Day/Night
‘Ibe sun goes far
‘WY
cycle.
switchesoff
mb)
Thesun
IlAb)
Cycle
DAY/NIGHT
CYCLE
133
modelsof thesecelestialbodiesare constrainedby ontologicalpresuppositions of the sort discussedby VosniadoudcBrewer(1992),thesepresuppositions alsoact asindirectconstraintson mentalmodelsof the day/nightcycle.
In this sectionwe will examinehow children’smental modelsof the earth
andthe sunconstraintheir mentalmodelsof the day/night cycle,The question about how the mental modelsof the moon and the starsinfluencethe
mentalmodelsof the day/night cyclewill be addressedin the next sections.
Initial Models
Basedon our studiesof individuals’ representations
of the earth,we assume
that childrenstartby forming a mentalmodel of a flat andstationaryearth,
supportedby something,usuallydirt and rocks. Giventhe mentalmodel of
a flat, supported,stationaryearth,the disappearance
of the sun canbe explainedby different mechanismsdependingon whetherthe sun is conceptualizedto be stationaryor moving. If children think that the sun moves
they canhypothesizethat at night it goesbehindmountains(Figure2,lAa)
or that it goesfar away (Figure2, 1Ab). If the sunis conceptualizedasstationary, childrencan hypothesizethat somethingelse(e.g., clouds,moon,
darkness,etc.)comesandcoversit up (Figure2, lBa), or that it switchesoff
,
(Figure2, 1Bb).
Thesemental models of the day/night cycle are called initial models
becausethey rely exclusivelyon interpretationsof experiencewhich can be
derivedfrom everydayobservations.The syntheticmodelsdiscussedbelow
showthe influenceof the’culturally accepted,scientific information about
the earth, sun, and the day/night cycle.
Synthetic and Scientific Models
The mental model of a flat, stationaryearthrootedin the groundseemsto
placestrongconstraintson a child’s understandingof the scientificexplanation of the day/night cycle. For example,it is difficult to conceptualizea
flat earththat is rooted in the groundas spinningor revolving aroundthe
sun.As childrencometo form a mentalmodelof a sphericalearthsurrounded
by space,an additionalclassof day/night mental modelsbecomeavailable
to them. Even whenthe sphericalearthis thoughtto be stationaryand the
sunasmoving, childrencanthink of the sunasgoingdownto the otherside
of the earth, or as revolving around the sphericalearth (Figure 2, 2Aa,
2Ab). On the other hand, childrenwho havebeenexposedto the scientific
information that the day/night cycleis dueto the rotational movementof
the earthcan conceptualizethe sphericalearth aseitherrevolvingarounda
stationarysun (Figure 2Ba), or as rotating around its axis (Figure 2Bb),
or both.
134
VOSNIADOU
AND
BREWER
Criteria for the Evaluation of Explanations:
Accuracy, Consistency, and Simplicity
Kuhn (1977)discusses
five criteria (or values)which scientistsuseto evaluate
the adequacyof a theory. Three of these,accuracy, consistency, and simplicity, seemto us to be good criteria by which to judgechildren’sexplanations of the day/night cycle.
A theory shouldbe accuratewithin its domain in the sensethat the consequences
deduciblefrom the theoryshouldagreewith the resultsof existing
observationsand experiments.In our casethis meansthat children’sexplanationsof the day/night cycleshouldbe consistentwith the empiricalobservationswhich arerelatedto the phenomenonof the alternationof day and
night (seeFigure 1). On the basisof the existingresearchfindings (Baxter,
1989;Sadler,1987),we would expectthat children’sexplanationswill indeed
demonstratesuchempirical accuracy.
Kuhn’s (1977)secondcriterion is the criterion of logical consistency.A
theoryshouldbeinternallyconsistentwith itself aswell aswith otheraccepted
theoriesabout relatedphenomena.Notice that researchers
who claim that
children’sexplanationsof phenomenaare fragmentedor looselyorganized
areassertingthat childrendo not adopt a principle of logical consistencyin
theorizingabout the physicalworld (see,e.g., disessa,1988,1993;Reif &
Allen, 1992;Solomon, 1983).
In our discussionof the constraintsthat the mental modelsof the earth
and the sun imposeon the mental modelsof the day/night cycle,we have
assumedthat children will show logical consistency.We assume,in other
words,that childrenwith thementalmodelof a stationarysunwill not choose
to explainthealternationof dayandnighton thebasisof thesun’smovement,
asin (Figure2) models1Aa and 1Ab or models2Aa and 2Ab. Similarly, we
expectchildrenwith mental modelsof a flat and stationaryearth will not
provideexplanationsaccordingto which the earthrotatesaroundits axis or
revolvesaroundthesun. Childrenwho saythat the sunor the earthis stationary in responseto questionsregardingthe movementof the sunandtheearth
and then go on to explainthe day/night cyclein terms of the movementof
the sun or the movementof the earth, are logically inconsistent.
It is logically possible,however,to’think that the sun movesbut not to
usethe movementof the sun as the mechanismto explain the day/night
cycle.This would meanthat the mentalmodels1Baor 1Bbin Figure2 would
still belogicallyconsistentmodelsfor a child who hadthe modelof a moving
sun. The interdependencies
betweenchildren’s mental models of the sun,
moon, starsand eartharerathercomplexandaredescribedin detail laterin
this article,whenwediscussthe criteriausedfor the derivationof children’s
mental modelsof the day/night cycle.What shouldbe stressedhereis that
our hypothesisthat childrenwill showlogicalconsistencymakesstrongpredictions about the relationshipsbetweenindividuals’ mental modelsof the
DAY/NIGHT
CYCLE
135
earth and the sun and their mental modelsof the day/night cycle, which
allow us to test this hypothesis.
A third criterion by whichto judgea theoryis, accordingto Kuhn (1977),
the criterion of simplicity-“ a theory should be simple, bringing order to
phenomenathat in its absencewould be individually isolatedand, as a set
confused”(Kuhn, 1977,p. 322).Wethink that it is possibleto decidewhether
childrenare sensitiveto the criterion of simplicity in their explanationsof
the day/night cycleby looking at the similarity of the mechanismsusedto
explainthe disappearance
of the sunduring the night and the moon during
the day.
If childrenthink that the moon and starsare causallyimplicatedin the
day/night cyclethen their mentalmodelsshouldincludean explanationfor
the appearanceof the moon and the starsduring the night and their disappearanceduring the day. If, in addition to empirical accuracy,children
strive for logical consistency,then they should usemechanismsto explain
the appearance
andthe disappearance
of the moon and starswhich obeythe
sameconstraintsasthosethat governthe appearanceand disappearance
of
the sun.
Logicalconsistencydoesnot require,however,that the samemechanism
is usedto explainthe appearanceand disappearance
of all celestialobjects.
Childrenwho think that the sungoesbehindthe cloudsat night, but that the
moon and starsswitch on and off are‘asinternally consistentas children
who usethe samemechanismto accountfor the disappearance
of the sun,
moon, and stars.Using the same mechanismto explainthe disappearance
of thesun,themoon andstarsduringthe alternationfrom dayto night, shows
sensitivitynot only to logicalconsistency
but alsoto simplicityof explanation.
To conclude,wehypothesizethat elementaryschoolchildrenwill be able
to provideaccurateandlogically consistentmechanisticexplanationsof the
day/night cycle.Wepredictthat theyoungerchildren’sexplanationswill be
in termsof the occlusionof the sunby clouds,the sunswitchingoff, thesun
movingbehindsomething,or the sunmovingfar away,dependingon whether
the sun is conceptualizedas stationaryor moving. We further predict that
theolderchildrenwill generatesyntheticandscientificmodels-accordingto
which the earthrevolvesaroundthe sun, the sunrevolvesaroundthe earth,
or the earthrotatesaroundits axis. In addition, our theoreticalframework
predictscertaininterrelationshipsbetweenchildren’smental modelsof the
earth,the sun, the moon and the starsand their mentalmodelsof the day/
night cyclewhich can provide important information aboutchildren’ssensitivity to issuesof simplicity of explanation.
Methodological
Issues
The methodologyusedin this studyis similar to themethodologydescribed
in Vosniadouand Brewer(1992).It consistedof askingchildrenquestions,
136
VOSNIADOU
AND
BREWER
someof which requireda verbalresponse,andotherswhichrequiredmaking
a drawing. Someof the questionsusedcould be answeredon the basisof
information derivedeitherfrom experienceor from instruction(e.g.,Where
is the sun during the day?Doesthe earthmove?).Other questionsrequired
explanationsof phenomenawhich cannotbe directly observed,and about
which children do not usually receivedirect instruction (e.g., Whereis the
sun at night? Whereare the starsduring the day?).Theselatter types of
questionshavethe potential of revealingthe kinds of mental modelsindividuals usegenerativelyto answernovel questionsand to solveunfamiliar
problems. .
Different setsof questionswereaskedabout the sun,the moon, and the
stars,and children’sresponsesto thesequestionswereusedas the basisfor
deriving information about their mental modelsof thesecelestialobjects.
The children werealsoaskedto explainthe phenomenonof the day/night
cyclein a separatesetof questions.Children’soverallmental modelsof the
day/night cycle.werederivedat the end by comparingeachchild’s mental
modelsof thesun,the moon, andthestarswith his or her explanationsof the
alternationof day andnight. Only thechildrenwho exhibitedlogical consistencyin their modelsand explanationswereconsideredto havean internally
consistentoverall mental model of the day/night cycle. The others were
placedin a mixed category.
METHOD
Subjects
The subjectsfor this study were60children:20 first graders,rangingin age
from 6 yearsand4 monthsto 7 yearsand5 months(meanage,6 yearsand9
months);20 third gradersrangingin agefrom 9 yearsand 3 monthsto 10
yearsand 3 months (meanage9 yearsand 9 months);and 20 fifth graders
rangingin agefrom 10yearsand 3 months to 11yearsto 9 months (mean
age11years).The childrenattendedan elementaryschoolin Urbana,Illinois
and came from predominantlymiddle-classbackgrounds.Approximately
half of the childrenweregirls and half wereboys. Thesesubjectswerethe
samesubjectsas thosein Vosniadouand Brewer(1992).
Materials
The materialsconsistedof a 48-item questionnaire.The questionnairewas
developedthroughextensivepilot work and wasdesignedto provideinformation aboutchildren’sknowledgeof certaincritical conceptsin astronomy,
including their ideasabout the earth’sshapeandgravity. Only the 13questions investigatingchildren’s ideasabout the disappearanceof the sun at
night, the movementof the moon, the explanationof the day/night cycle,
and the disappearance
of the starsduring the day will be discussedin this
paper. These questionswere selectedfor their potential to differentiate
DAY/NIGHT
Questions
Used
to Investigate
CYCLE
TABLE 1
Children’s
Mental
137
Models
of the Day/Night
Cycle
The Disoppeoronce
of the Sun ot Night
Where is the sun at night?
422:
Q23:
HOW does this happen?
Q240:
Does the earth move?
Q24b:
Does the sun move?
Explortoflons
of the Doy/Nlght
Cycle
[The experimenter
drew o circle to depict
left side of the circle.]
425:
Q26o:
the earth
and placed
a flgure
on the upper
Now make It so It Is day for that person.
Good1
Now make It so It Is night for thot person.
Tell me once more how thls happens.
The Movement
of
Q30:
Does the
Q31:
Does the
Q32:
Does the
Why does
Q33:
the Moon
moon move?
moon move along
moon move when
the moon move?
wlth you when
you are asleep
you go for a walk?
In your bed?
The Dlsappeoronce
of the Stars During the Day
Q36o:
Where are the stars at nlght?
Q36b:
Where are they during the day?
Do the stars move?
Q37:
,
amongthe different mental modelsof the day/night cyclepreviouslydiscussed.The 13 questionsare given in Table 1.
Questions22 and 23 (Whereis the sun at night, How doesthis happen?)
provideinformation about children’sexplanationof the disappearance
of
the sunat night. Questions24aand24b(Doesthe earthmove?andDoesthe
sun move?)revealedchildren’sknowledgeregardingthe movementof the
earthand the sun. This information was necessaryto allow us to test our
predictionthat children’sbeliefsabout the movementof the earth and the
sufiwould constraintheir choiceof mechanismto explainthe disappearance
of the sun at night.
The next set of questions(425, Q26a)requiredan explanationof the
alternationof day and night. Weexpectedthat theseexplanationswould be
basedon the belief that the day/night cycleis causedby the appearance
and
disappearance
of the sun.If the childrensawthe appearance
and disappearanceof the moon and the starsas causallyrelatedto the day/night cycle,
theyshouldprovidean explanationof the disappearance
and appearanceof
the moon and the starsas well.
The questionsabout the movementof the moon (430, 431,432, 433)
andaboutthe disappearance
of the starsduringthe day (Q36a,Q36b,437)
weredesignedto provide further information about the relationshipthat
childrensawbetweenthe sun,the moon andthe stars.This information was
138
VOSNIADOU
AND
BREWER
intendedto enableus to understandchildren’smental modelsof the day/
night cycleandto judgewhetherthesemodelswereempiricallyandlogically
consistentand showedsensitivityto issuesof simplicity of explanation.
Procedure
The childrenwereseenindividually in an interviewwhich lastedbetween30
and45minutes.Theexperimenter
madedetailednotesof children’sresponses.
The interviewwasalsorecordedusinga tape-recorder.The scoringwasdone
later on the basisof both the transcribeddata andthe experimenter’snotes.
scoring
The datawerescoredby two independentjudgeswho examinedthe four sets
of questions(the disappearance
of the sun at night, the alternationof day
and night, the movementof the moon, and the disappearance
of the stars
duringthe day)separately,assigningchildrento variouscategoriesof explanations.All disagreements
werediscusseduntil consensus
wasachieved.Our
previouswork (Vosniadou& Brewer,1992,pp. 54%547,554-555)hasshown
high reliability for classifyingchildren’sresponses
to thesetypesof questions.
In assigningchildren to mental modelswe followed a proceduresimilar to
that describedin Vosniadouand Brewer(1992).First, we identified, on the
basisof our dataandpreviousresearchin this area,a seta possibleexplanations for the disappearance
of the sun or the stars,of the movementof the
moon, etc. Then, we generatedthe pattern of responsesto our questions
which would be expectedassumingthat the childrenusedeachexplanation
consistentlyto answerall relevantquestions.Wethen checkedthe expected
patternof responses
againstthe patternof obtainedresponses
to the relevant
questions,and assignedchildren to various categoriesof explanations.If
the children were not logically consistent,they wereplaced in the mixed
category.
After we classifiedeachchild’s responses
to the four setsof questions,we
examinedthe four setsof responsescombinedand assignedchildrento an
overallmental model of the day/night cycle.At the end, we checkedto see
whetherthe derivedmental modelsof the day/night cycle wereconsistent
with children’smental modelsof the earth which had beenderivedin our
earlierpaper. The derivationof the mental modelsof the day/night cycle
wasdoneindependentlyfrom and without knowledgeof children’smental
modelsof the earth.
The detailedcriteria usedfor assigningchildrento a categoryof explanation for the four setsof questionsaredescribedin Table2 andarediscussed
in the next section.
RESUT.iTS
In this sectionwepresentthe criteriausedto assignthe childrento the various
categories
of explanationsof thedisappearance
of thesunat night,thealtema-
DAY/NIGHT
CYCLE
139
tion of the day andnight, the movementof themoon, andthe disappearance
of thestarsduringthe day.Thenwepresentthe criteriafor assigningchildren
to overallmental modelsof the day/night cycleand discussthe consistency
betweenmentalmodelsof the day/nightcycleandmentalmodelsof the earth.
Logical consistencyin children’sresponses
to thevariousquestionswasa
necessary
requirementfor beingassigned
to an explanationtype.The response
patternsjudgedaslogicallyconsistentfor eachsetof questionsaredescribed
below.
The Disappearance of the Sun at Night
Four questionswereaskedto determinechildren’sexplanationsof the disappearance
of the sunat night. Thesequestionscanbe found in thetop row
of Table 2. Children’s answersto thesequestionswere classifiedinto 11
explanationtypeswhich areshownin the first column of Table2. The first
explanationtype attributesthe day/night cycleto the occlusionof the sun
by cloudsor darkness.Explanations2 to 6 focus on the movement of the
sun asthe primary reasonfor its disappearance,
while,explanations7 and 8
usethe movement of the earth asthe primary reasonfor the disappearance
of the sun at night. The body of the table contains,for eachquestion,the
typesof responsesthat wereclassifiedasinstancesof eachexplanationtype.
Responses
to Question24b, “Does the sun move?“, werecritical in differentiatingthe childrenwho attributedthe disappearance
of the sunto the
movement of the sun from thosewho attributed it to the movement of the
earth. Children assignedto explanationtypes 2 to 6 were expectedto say
that thesun movesup/down or east/west.Childrenassignedto explanation
types7 and 8 wereexpectedto say that the sun is stationaryor to mention
movementsthat could not be usedto explainthe day/night cycle(e.g.,that
thesunrotatesaroundits axisor movesdueto theexpansionof the universe).
Responsesto Question24a, “Does the earth move?” were critical for
assigningchildrento explanations7 and 8. For explanation7 the children
wereexpectedto say that the earthturns, spins,goesaround in circles,or
movesand for explanation8 that the earthgoesaroundthe sun.Affirmative
responsesto question24a “Does the earth move?” were not considered
inconsistentwith explanations1 to 6 becauseit is possibleto havea model
of the earthmoving which doesnot explainthe disappearance
of the sunat
night. Ideallywe expectedthat thechildrenwho attributedthe disappearance
of the sunat night to the sun’smovementwould saythat the earthis stationary. However,many childrenwho areexposedto the information that the
earthmovesdo not understandexactlyhow the earthmovesor do not realize
that this movementhasany explanatorypowerwith respectto the alternation
Ofdayandnight. It is possibleto constructvariousmentalmodelswherethe
movementof the earthis not logically inconsistentwith the explanationof
the disappearance
of the sunbasedon the sun’smovement(e.g.,the earth
moves/shakesasin an earthquake,or that the earthmovesrotationally but
very slowly-once during a year, and so on).
of Explanation
by
Down
5. The sun goes
unspecified
12. 0. 0=2)
down,
Below the earth;
under
the earth;
down to the
other side of the earth
4. The sun goes down to
other side of the earth
(2, 0, 1=3)
In space
Behinds clouds
In darkness
In the sky
is the sun at night?
far the Disappearance
The sun moves down
on/in the ground;
moves
down behind hills,
mountains,
in the water
in and
b
Where
Q22
Types
3. The sun goes down
on/in the ground
(6, 1, 1=8)
2. The sun moves
out of space
(1, 1,0=2)
1. The sun is occluded
clouds or darkness
(2,2,
1=5)
Type
Explanation
does
this
out into
down
way
The sun goes down; it
goes to another
country
The sun moves down to
the other side of the eorth
The sun moves
The sun goes
space
cover
happen?
Clouds or darkness
the sun up
How
Q23
TABLE 2
of the Sun at Night Questions
the earth
Frequency
No or Yes
No or Yes
No or Yes
No or Yes
No or Yes
Does
Q24a
and Their
move?
as a Function
Yes,
Yes.
Yes,
Yes,
it moves
it moves
it moves
it goes
space
up/down
up/down
up/down
into
the sun move?
Yes or No
Does
Q24b
of Gradea
a n=60
Undetermined
(3, 4, 027)
(1, 2, 3=6)
and
of the
TABLE
made
earth
way
around
inconsistent
it that
goes
the
for each grade.
across
grades.
No response,
do not
know,
irrelevant
or
ambiguous
response
Logically
resuonses
God
The
sun
around,
rotates,
goes
in circles,
or moves
turns
turns,
the
spins,
around
around
2 (Continued)
goes
Earth
The sun
earth
of explanation
type
gives the frequency
where
it is or on the
side of the earth
give the frequency
5. The last number
Anything
Anything
b The numbers
in parentheses
Grade
3, and the third for Grade
11.
10. Mixed
day
Anything
2=3)
9. God made
night
(0, 1, O=l)
(0.1,
Stays
other
(3, 7, 12=22)
8. The earth revolves
around
the sun
side
where
it is or on the
side of the earth
Stays
other
7. The earth turns
the sun is fixed
and
At the other
earth
6. The sun revolves
around
the earth
(0, 1, O=l)
The first
number
No or Yes
Inconsistent
No
Yes it goes
sun
moves
the
is the frequency
responses
around
Yes; earth turns,
spins,
goes around
in circles
or
No or Yes
around
the
above
far
Grade
Yes or No
Inconsistent
No
As
1, the second
responses
for
No or if Yes only axis
rotation
or movement
due
to expansion
of universe
Yes, it goes
earth
142
VOSNIADOU
AND
BREWER
Information abouthow children’sresponsesto Questions22and 23were
usedto assignthem to the specificexplanationtypesis presentedin Table2,
which alsoshowsthe frequencyof theseexplanationsasa function of grade.
Table3 givesa protocolexamplefrom eachexplanationtype.A moredetailed
discussionof certain aspectsof the classificationsis given below.
The critical information for placinga child in explanationtype4 (sungoes
down to the other side of the earth) was the useof phrasessuchas below,
under, or down to the othersideof the earthto Question22, “Where is the
sunat night?Thesephraseswereusedto distinguishexplanationtype4 from
explanationtype 3 (the sun goes down on/in the ground). Two childrendid
not give enoughinformation in their responsesto Questions22 and 23 to
determinewhetherthey believedthe sun stayson the groundor whetherit
goesdown,to the othersideof theearth.For example,Jeff (protocolnumber
5, Table3) saidthat the sun goesdown “to a city or something.”This city
could be on the sameside or on the “other” side of the earth. Thesetwo
childrenwereplacedin explanationtype 5 (the sun goes down, unspecified).
In explanationtype 6 (the sun revolves around the earth), the earth is
consideredfixed and the sun revolvesaround it. The one child who was
placedin this categorythoughtthat the sunandthe moon “trade places” as
they revolvearoundthe earthevery24 hours.This child statedthat the sun
is “on the other side of the earth” to Question22, “Where is the sun at
night?“, because“the sun goesaroundthe earth” (Question23). Seeprotocol number 6, Table 3 for more details.Note the interestingcontrastof
explanationtype 6 with explanationtype 8 (the earth revolves around the
sun) in which the sun is consideredfixed and the earth revolvesaround it.
Thereweresomechildrenwho could not be classifiedinto oneof the nine
explanationtypes.A patternof responses
wasscoredasexplanationtype 10
(mixed)whenmore than onemechanismwasusedto explainthe disappearanceof the sun at night, thus resultingin an internally inconsistentmodel,
For example,Sandra(protocolnumber 10,Table 3) startsby explainingthe
disappearanceof the sun in terms of the up/down movementof the sun,
continueswith an occlusionexplanation,and whenaskedwhetherthe earth
moveschangesto an earthaxis rotation explanation.A numberof children
wereclassifiedas explanationtype 11 (undetermined). The childrenplaced
in this categoryeithersaid that they did not know how to explainthe phenomenonin questionor gavean explanationwhichwe couldnot understand.
An exampleof one of the undeterminedresponsesis givenin Table 3 (protocol number 11).Many of the mixed andundeterminedresponsesrevealed
children’sattemptsto keepelementsof their initial explanations(usuallyin
termsof an occlusionor sunmoving up/down mechanism)astheyreplaced
them with the culturally acceptedexplanationof a rotating earth.
Examination of Table 2 showsthat, as was expected,most of the firstgradechildrenprovidedexplanationsin termsof the initial mentalmodelof
by clouds
down,
unspecified.
(No. 45, Grade
1)
Where
is the sun at night?
Down there.
Where’s
there?
It goes down.
Down where?
It goes to a city or something.
Does the earth move?
No.
Does the sun move?
Yes.
goes
The sun
5.
Jeff
E:
C:
E:
C:
E:
C:
E:
c:
E:
C:
Tomara
(No. 3, Grade
5)
E: Where
is the sun at night?
c: It’s hiding.
Where’s
it hiding?
E: It’s hiding?
c: I don’t know.
. .cause
it won’t
shine.
E: How does this happen?
c: The clouds block it.
E: Does the earth move?
c: It goes around.
It goes east,
west,
north.
E: Does the sun move?
c: Yes.
1. The sun is occluded
or darkness
in and
out of
of Explanations
sun
revolves
around
the
earth.
goes
of the
down
the
7.
Sun at Night
on/in
Betsy (No. 53, Grade
1)
E: Where
is the sun at night?
C: Down.
E: Down where?
C: Below the hills
E: How does this happen?
C: I don’t know.
E: Does the earth move?
C: No.
E: Does the sun move?
C: It goes up and down.
3. The sun
ground
TABLE 3
of the Disappearance
Koren (No. 37, Grade
3)
E: Where
is the sun at night?
C: Well, it goes under the earth to Chino. See, while we have day,
China has night and while China hos night, we have day.
.
E: How does this happen?
C: Well, the moon and the sun trade places every.
. . I guess it’s. . .
E: Do you mean 24 hours?
C: OK, every
half of 24 hours they will change,
they trode.
Like they
. . . in the a.m. the sun is here..
.for 12 hours and the moon is in
China for 12 hours.
And when China has sun for 12 hours,
we have
the moon for 12 hours.
E: Well, does the sun move then?
C: Oh yes, it moves
every
hour. Well, every yeor, yoa. It moves very
slow. Every year it moves
a little bit, but it moves
slowly
and uhmm,
every
year it’s gone around
once.
E: It’s gone around
what?
C: The sun has gone around
the earth once..
.every
year. Well, not
once. . . it goes around
every
year, the sun does. But the earth
moves
around
in a circle every
year.
E: Does it move oround
anything?
C: To me, everything
moves oround
the earth,
and it doesn’t
move
around
anything.
6. The
Kristie
(No. 52, Grade
1)
Ez Where
is the sun at night?
c: Gone in space.
E: How does this haooen?
goes way
C: When it get dark’it
into space.
E: Does the earth move?
c: Yes, the earth just floats.
E: Does the sun move?
c: Yes
moves
Examples
2. The sun
space
Protocol
turns
ond
the
sun
is fixed.
(continued)
Cindy (No. 29, Grade
3)
E: Where
is the sun at night?
C: On the other side of the earth.
Because
when night comes
over here the sun goes onto
the other side of the earth
and it’s day on there.
E: How does this happen?
C: The earth turns around.
E: Does the earth move?
C: Yeah.
E: Does the sun move?
C: No.
The earth
Brian (No. 43, Grode
1)
Ez Where
is the sun at night?
C: Under the earth.
E: How does this happen?
C: Because
the moon comes out
and the sun comes down.
E: Does the eorth move?
c: No.
E: Does the sun move?
C: Yes, it goes down.
4. The sun goes down to the
other side of the earth.
E
8.
The
around
3)
the
sun.
9.
God
E:
c:
E:
c:
E:
c:
E:
c:
E:
c:
day
3)
night.
3 (Continued)
and
21, Grade
made
(No.
TABLE
Where
is the sun at night?
h’s in another
land, or mwbe
another
How does this happen?
.
It’s the way the earth is made.
Can you explain
this move?
It’s just the way God created
it.
Does the earth move?
No.
Does the sun move?
No.
’ Jamie
Charles
(No. 36, Grade
3)
E: Where
is the sun at night?
C: Behlnd the moon.
E: How does this happen?
C: The earth is rotating.
The earth is going around
in
circles
on its axis. And it’s making
the sun move toward
the moon.
It looks like it because
the earth is rotating.
E: Does the earth move?
c: Y&s.
E. Does the sun move?
C: Some, maybe,
yes.
11. Undetermined
c:
E:
c:
E:
c:
E:
E:
c:
revolves
39, Grade
earth
(No.
Where
is the sun during
night?
On the other side of the earth.
How does this happen?
The earth moves
around
and it has a line
and the sun keeps
going around
that,
around
the earth..
. l mean around
the sun.
Now wait,
I just got a little confused.
How
does the earth move again?
It moves
around
the sun..
.
does the sun move?
No.
Now, what’s
that thing about the line?
Well, the line is like a path that it just keeps
going around,
it doesn’t
go back and forth.
Isaac
_,
planet.
lO.Mixed
(No,
27, Grade
3)
E: Where
is the sun during
the night?
C: It went down to the moon.
E: How does this happen?
C: Because
at 5 o’clock
the sun sets and it rises
in the morning
and sets at night. It goes
down when it has to.
E: Why does it have to?
C: Because
it sun, it’s night and day and it’s
supposed
to be night around
5 or 6 o’clock
and day around
1 or 2 or 3 o’clock.
E: So is the sun moving?
C: Yes.
E: Can you tell me how it moves?
C: l don’t think it really moves,
but I think the
clouds
just cover
it all up.
E: Does the earth move?
C: No.. .the earth do move I mean.
E: How does the earth move?
C: Because
it rotates
around,
and that’s how the
sun goes down,
because
the earth is turning
to one half and the other half be day and it
wait for 24 hours and it turn to the other half.
And this half be night and this half be day.
Sandra
DAY/NIGHT
CYCLE
145
a sunmoving down on the ground,whereasmost of the older childrenprovidedexplanationsin terms of the rotational movementof the earth.
The Alternation
of Day and Night
Children’sexplanationsof the alternationof dayandnight weredetermined
on the basisof their responsesto Questions25 and 26a,which areshownin
Figure3. For Questions25,the experimenterdrewa circleto depictthe earth
andplaceda figure on the upperleft sideof the circle. Shethensaid, “Make
it soit is day for thisperson”andthen“Make it soit is nightfor this person.”
In Question26aa verbalexplanationof the day/night cyclewas requested
(“Tell me oncemore how this happens.“)When assigningchildrento categoriesof explanationswe looked at the consistencybetweentheir drawings
andtheir verbalexplanations.Childrenwereplacedin an explanationcategorywhenthe drawingandtheir verbalexplanationindicatedthat the same
mechanismwasusedto explainthe day/night cycle.Neutraldrawings(e.g.,
thechild simply crossesout the sun,asshownin Figure3, ExplanationType
6) were acceptedif the verbal explanationwas unambiguous.Similarly,
neutralverbal explanationswereacceptableif the drawingwas unambiguous. If the drawing and the verbal explanationwereboth ambiguous,the
child’s responsewas placedin an undeterminedcategory.If they wereinconsistentwith eachother (in that they implied the useof different mechanisms),the child was scoredas mixed.
Whenthe decisionwasmadeto usethe drawing of a circle to depict the
earthwith a figureplacedon theupperleft sideto depictthe peoplewho live
on the earth we had not yet understoodchildren’s mental models of the
earth.This drawingturned out to be somewhatproblematicbecausesome
of the childrenwho participatedin this studydid not think of the earthasa
sphere,or did not believethat it is possiblefor peopleto live on the surface
of this sphere.Some children in our samplebelievedthat the earthis flat
like a rectangleor like a disc, or a hollow spherewith peopleliving on flat
grounddeepinside it (seeVosniadou8cBrewer, 1992).
As will becomeclearin the protocolexamplespresentedin Table4 andthe
drawingspresentedin Figure3 and Figure4, someof.the childrenexplicitly
rejectedour drawingandput their figureinsidethe circle,on a flat line inside
thecircle,or on a flat line underneaththecircle. Othersdid not sayanything
but ignoredthe drawing and madetheir own. In somecases,however,the
drawingand the placementof the figure may haveresultedin pictorial representationsof the day/night cyclewhich wereinconsistentwith the verbal
explanationsor which did not reflect them accurately.We tried to take the
child’spoint of viewinto considerationasmuch aspossiblewheninterpreting
the drawings,but in a few caseswe may haveplacedchildrenin the mixed
categorywhenthey did not actually belongthere. We could have decided
not to usethe drawingdata,but had wedoneso, muchinterestingandvaluable information would have beenlost in order to eliminate a relatively
small numberof problematiccases.
= 1)
3. Explanations
lllcslmgaudmmfotbcorsidc
ofthcca&(andtbcmamwmaup)
(4.0,0=4)
lltcsungocsdmvnwinlhcgmund
(drht-g=~P)
(1.1.0-2)
ThcSWlObOVUiolOspacc
(1.0.0
llwsunbacckkdbycbDdsor
Figure
day/night
cycle.
mskcitsoitbdayforlbslpcrxm
of the
and
their
frequencies
of grade.
Iolbcc4K?si&ofIbce(sndlbe
TtlCSUlgOUdOWllUldCXIbCeanhor
-fb.smlgoudown~nIhcgmmKt
(ovcrlhchill,intiwsw)andtbc
mm coma up
llh?slmgouinlospaccaodcomu
CbUd3or&anigb1covcruplbc
OS a function
Thesongocsdown-tmspccif~~wiih
-rhecmhmvolvusmlmdlhcslm
mlcurlhfJmsup/dovmandrheslm
is fd
(moon mtqlccified)
9
rtspmlOlXUlhSid0
8
6
T)pz of Explanation
soilisdayforlhalp
make it so it is night for
1tgoesloanolhu
The sun slays in one place
llu.eanhtumsamuwJ(spinsormfau9)
lllcc.mhgoes(mrm)aIolmdIhcsml
mslmgocsdown
moon
3 (Continued)
is the frequency
for grade 1, the
No response. irrelevant or ambiguous
The earth turns around (spins or rotate)
When lhe earLh pf3 around its orbit,
this side becomes day and hii side becomes
‘Ihe earth turns away from the sun
When il is daylime tbe cailh turns (spins
ormtatcs)amuodtbestm.
Whmitis
nighttime. it turns to where the moon is
type for each grade. The first number
gives the frequency across gradn.
nse, irrelevant or ambiguous
bThc numbers in parentheses give the frequency of explanation
second for grade 3, and the third for gade 5. Thc last number
an=60
(2,2,2=6)
12 Tbecanhtumssi&waysandtks
andmomlamfmYJatoppositesidcs
11 lkcanbtumssi&ways
lwpccirvd
(0.3.5-8)
aodmoonarcfiicdatoppositesides
Figure
DAY/NIGHT
CYCLE
149
Finally, it shouldalsobementionedthat children’sresponses
wereplaced
in themixed categoryif at any otherplacein the interviewtheyprovidedan
explanationof the day/night cyclewhich was different from the one they
gavein responseto Questions25and 26a.Suchopportunitiesexistedat differentpartsin the interview, for example,whenchildrenwereaskedabout
theapparentmovementof themoon, or the disappearance
of thestarsduring
theday.The strict criteriafor internalconsistencyweemployedmay explain
the relativelarge number of mixed casesfor this set of questions(11/60).
The exact criteria for assigningchildren to eachexplanationtype are
givenin Figure 3 and will be further discussed.Figure 3 alsoshowsthe frequencyof children’sexplanationsasa function of grade.Protocol examples
for eachexplanationtype canbe found in Table4 (pp. 150-151).The drawings of the children whose protocols were usedin Table 4 are shown in’
Figure4 (p. 152).
In explanationtype 1 the sunis occludedby clouds,while in explanation
type2, daygoesawayandnight takesits place.Explanationtype2 doesnot
useocclusionasthe mechanismfor the disappearance
of the sunbut rather
the movementof thesun (aswell aseverythingelsethat constitutesday)to
anotherplace.
In orderto be placedin explanationtype4 (thesungoesdown on/in the
ground)a child had to provide someevidence,either in a drawing or in a
verbalstatementor in both, that the sungoesdown on or in theground(not
down to the other sideof the earth). Statementssuchas “on” or “in the
ground” “behind hills, 3’ “in the water,” etc. were used by the children
togetherwith drawingswhich depictthe sungoingdownbut not to theother
sideof the earth.
Children’sdepictionsof the sun going down on the ground variedconsiderably.As shownin Figure3, somechildrenplacedthesuninsidethe circle
depictingthe earth (Figure3, explanationtype 4, drawingsa and b). There
werea variety of other options.In drawingb the child drewanothersunto
indicatethe downwardmovement.In drawing c the child showedwith an
arrow how the sun goesdown to the ground. In drawingd we havea child
with a two-earthmodel who showedthe sun going down towardsthe flat
groundwhich is supposedto be below the sphericalearth.Thesedrawings
showthat the way children conceptualizethe movementof the sun varies
greatlydependingon their mentalmodel of the earth,but theexactrelationship betweenmentalmodelsof the earthand mentalmodelsof the day/night
cyclewill be discussedlater in this article. Finally, it is important to note
that all but oneof the childrenplacedin this categoryimplicatedthe moon
in the day/night cycle by sayingthat when the sun goesdown, the moon
goesup.
The crucial differencebetweenexplanationtype 5 (thesun goesdown to
theotherside of the earth)and explanationtype 4 is that the childrenprovided evidenceeither in their drawing or in their verbal statementsor in
Allison (No. 52, Grads 1)
Autumn (No. 51, Grade 1)
E: Now make it d-q for that pman.
c: Sun and clouds in the sky.
Ralnbaw, mlndrop (see drawing
2 in Figure 4).
E: Now make it so It is night for
that pwsa”.
c: Everything goes away.
E: Can you make II night?
c: How?
E: Go ahead and draw It in.
How *ould it be?
c: The stuff would go away
E: Da you know we,. It would go?
C: Into another place.
E: Da you know bow that happens?
C: Yes. Urn the night takes aver
the *un.
Tamam (No. 9, Grade 5)
E: Now can you make It so it Is day
for that person?
c: He’s outside the earth.
E: Where should he be?
c: In hero (see Figure 4, drawing 1).
E: . . .OK now. make It daylime
for him.
c: The .un is out here. but It looks
like it’s In the earth, when It
shines.. .
E: OK. What happens at night?
c: The clouds covered it up.
E: Tell me once more hw, it
haPP-C: Cause ol 12 o’clock It’s dark.
E: Now make it so It is day for that
perwn.
C: (child makes drewlng 3 shown in
Figure 4) Right here?
E: Whatever you think. Now make
It nigh.
c: It gaea in space.
E: Show me. Tell me how It happens.
OThesuncamolbackdawn.It
goes into space and when it gets
dark the moan comes back out.
3. The run mover auf into space.
1. The sun Is occluded by clouds or
darkn~.
2. Day Is replaced by night.
TABLE 4
Protocol Examples for Explanations of the Dcy/Nlght
E: Can you make it day for this
pe-?
c: (see drawing 4 In Figure 4)
E: Now make it night for that
person.
c: To make It night, erase the sun
and r+ca
It with the moan.
E: Can you tell me once mare how
It bappelr?
C:The.ungaesdawnondthemaon
comes up, and then the moan
goes davm and the sun coma up.
E: Where Is the moan when the sun
Is up?
c: The maanir where the run rests.
Harmony (No. 41, Grads 1)
4. The sun gaea dawn on/in the
ground (and the moan comes up).
Cycle
shown
E: Tell me once mere how it
hOppll%
c: When the moan tamer up and
the sun goes dawn.
E: W-tare war the moan before?
c: Under the earth.
E: who, time was It when It goes
under the earth?
c:Day.
The child makes the dmwlngr
in Flgun 4.
Tlmathy (No. 47. Grade 1)
5. Thewngaesdawltotheothw
IIda of tha earth (and tha moan
gon UP).
and the sun Is fixed
Eddie (No. 20. Grade 5)
C: (Child makes dmwlng 11 shown In Fl&tre 4)
E: Tell ms how It happnr.
c: Catle when the earth turns away from the sun, it gets dark.
11. The earth rotates Ieft/rfght
(moon unspecified).
Karen (No. 37, Grads 3)
The child makes drawing 7 shown
Figure 4.
Quinten (No. 44, Grade 1)
E: Now make it day. Now make It
night.
c: (see dmwing 6 in Figure 4)
E: Tell me onca more how this
happwts.
c: Because he’s on top of the earth
and the sun’s going to ba coming
out of the whole *pace. The sun’s
supposed to be in the mkidle of
the whole part.. .rmd It coma
out. Then he’ll ba rtandlng on the
earth so he’ll ga to sea the sun.
And when the moon comes, he
con see the moon too.
E: Does the sun move?
c: Only up and down.
E: Does the moon mow up and
dwm too7
c:Ye,
Venlka (No. 33. Grade 3)
C: (Child makes dmwlng 12, Flgure 4)
E: Can you tell me how this hoppens?
c: when the earth turns around Its orbit, this rl&
and the other ride comes night.
and
comes day
Robert (No. 5. Grade 5)
E: Now make it sa it is day for
tflat person.
c: (child makes drawing 10 sbovm
In flgura 4)
E: Now can you make it nighttime?
C: Can I draw him somewhere else?
(draws figure at the bottom
of the earth)
E: sure.
c: (Child dmvn arrows to show
how earth spins)
E: Tell me bow it hoppens.
C: when It was dayiime. the earth
spinnd around to the sun.
Wlwn it was nighttime. the
earth turned around to where
the moon Is.
10. The earth rotates up/down and
the *un and moon ore fixed at
opposite rida.
Joshua (No. 1. Grade 5)
c: (Child produces drawing 13. Figure 4)
E: How does this happen?
c: Cause Lo world rotates.
13. The earth rotates in unspecified direction,
moon unrpecifled.
E: Tell me how It happens.
c: The sun stays In one place mid
the earth turns.
E: How?
C: It turns around.
Chd (No. 19. Gr&
5)
Child makes dmwlng 9 shown in
Agur.4.
9. The earth rotates up/down
the run is fixed
(moon unspectfied).
and the sun and moon ore
Mike (No. 11, Grade 5)
E: Make it so It’s day time for this
pemn
c: (roe drawing 8. Ffgure 4)
E Make it so It’s nIgftt.
c: Moon (child draw moon)
c: Tell me once more how It
happens.
c: The earth turns around the sun.
and the sun gives heat.
8. The earth revohres around
the sun.
12. Tb. earth rotates left/right
fixed at opposite alder.
E Now make it so it Is night.
t: We hove to cross out the sun
and put it over here.
E: Tell me once mom how it
haPpen,.
c: Well. the sun vibrates around
the earth every 12 hours. And
then the moon goes the other
dlrectlon and vibrates wound
the earth every 12 hours.
50 both us and Chlna have
the moon and the sun.
7. The run and the moon revolve
around the earth.
6. The run goa down, unspacified
as to whkh ride of the earth
bd the moo” wea UP).
TABLE 4 (continued)
Drawing
Drawing
No. 4
No. 1
Figure
4. Drawings
od
of children
ore
9
Drawing
No. 2.
protocols
Drawing
whose
as examples
No. 5
given
of explanations
of the
No. 3
No. 6
Drawing
cycle.
Drawing
day/night
L
d
153
154
VOSNIADOU
AND
BREWER
both, that the sun wentdown to the other side of the earth. The three children
placedin this categorymade drawingssuchas the one shownin Figure 3,
depictingthe sun going down to the other side of the earth, and also said
that the sungoesdown,under,or to the othersideof theearth.Two of these
childrenalso saidthat the moon goesup whenthe sungoesto the otherside
of the earth.An exampleof this typeof responseis protocolnumber5, Table
4 and drawing number5, Figure 4.
In explanationtype 7 (the sun and the moon revolve around the earth),
the alternation of day and night is causedbecausethe sun and the moon
revolvearoundthe earth every24 hours. Sincethe sunand moon are conceptualizedasbeinglocatedat two diametricallyopposedsidesin their orbital
path, this explanationnicely accountsfor the alternationof day and night
for the different parts of the earth.
The criteria for explanationtype 8 (the earth revolves around the sun)
wereeither an unambiguousdrawing showingthe earth revolving around
the sun or a verbal explanationindicating revolutionarymovementof the
earth,or both. Note that the model accordingto which a nonrotatingearth
revolvesaround the sun in 24 hours generatesthe appropriateday/night
cycle. Children who gavea revolution explanationbut a rotation drawing
wereplacedin the mixed category.The four childrenplacedin this category
saidexplicitly that the earthgoesaroundthe sunin their verbalexplanations
and madea drawingwhich was not inconsistentwith this explanation.An
exampleof this type of responseis protocol number8, Table4 and drawing
number 8, Figure 4.
Explanationtype 9 (the earth rotates up/down and the sun isfixed) is one
of a classof rotation explanationswhich is characterizedby the up/down
rotationof theearth(Le.,rotationaroundan axisthroughthe equatorinstead
of through the poles).The childrenplacedin this categoryail said that the
earth turns around and the sun staysin one place.Information about the
directionof the rotation wasobtainedfrom their drawings.Up/down rotation wasindicatedeitherwith an arrow or by placingthe figureat the bottom
of the earth to make it night time (seedrawingsa and b respectivelyfor
explanationtype 9, Figure 3). An exampleof this type of responseis given
in Table4, protocol 9 and Figure4, drawing 9. Childrenwho saidthat the
earthturns, spins,or rotatesbut madea neutraldrawingwith respectto the
direction of rotation wereplacedin explanationtype 13.
Examination of explanationtype 9, Figure 3, showsthat thereis another
possibleinterpretationof the up/down arrow. One could imaginethat one
is viewingthe earthfrom abovethe north poleandthat the figureis standing
on the equator. If one adoptsthis perspectivethen the arrow that we are
interpretingas “up/down” would actuallybe west/east(i.e., rotationaround
a polar axis).Weunderstandthat this is a logically consistentinterpretation
of the drawingby an adult. However,our experiencewith childrencarrying
out the drawingtask suggeststhat theyinterpretthe figure in our drawingas
DAY/NIGHT
CYCLE
155
standingon the “top” of the earth(Le.,at the north pole). It is possiblethat
this preferenceis relatedto problemschildrenhavewith gravity.In addition,
wehaveunpublisheddatain whichchildrenaregivena spherewith a person
on it andareaskedto makeit dayor night for the figure.Whenmanipulating
themodelsthe childrentendto carry out an up/down rotation, not a west/
eastrotation of the earth. On the basisof these‘observations,we haveconcludedthat the bestinterpretationof the type of drawingsgivenin Figure3,
explanationtype 9, is up/down rotation.
Explanationtype 10 (the earth rotates up/down and the sun and moon
are fixed at opposite sides) is similar to explanationtype9 with the additional
constraintthat the sunandmoon arefixed at two oppositesidesof theearth,
The information that the sun and moon are fixed at oppositesidescould
comeeitherfrom an unambiguousverbalexplanationor from an unambiguousdrawing or from both. The drawingsexpectedfor this explanation
typeareshownin Figure3 and areof two kinds: (1) they depictthe sunand
themoon fixed at the top andbottom of the earth at least90” apart, or (2)
theydepictthe sunand themoon to be fixed at the left andright sidesof the
earthat least 90’ apart and indicateup/down rotation of the earthby the
useof an arrow or by the placementof figureson the bottom parts of the
earth.This additional information is requiredwhen the sun and the moon
arefixedat the left and right sidesof the earthbecausein this casetheir position alonedoesnot provideinformation aboutthe directionof the rotation.
An exampleof oneof theseresponsesis protocol 10,Table4, and drawing
10,Figure4.
Thereweresomechildrenwho could not be classifiedinto oneof the 13
explanationtypespreviouslydescribed.Thesechildrenwereplacedeitherin
explanationtype 14 (mixed)or in explanationtype 15(undetermined).The
childrenplacedin explanationtype 14 (mixed) providedevidencefor two
conflictinginterpretationsof the day/night cyclein their responses.Sometimesthe conflict existedin the inconsistencybetweenthe drawingand the
verbalexplanation,suchasin subjectnumber15,who drewan arrow showing theearthto rotateup/down but saidthat the earthturns aroundthesun.
At othertimes the conflict existedin the inconsistencybetweenchildren’s
responses
to Questions25 and26a,andwhat wassaidlaterin the interview.
For example,subjectnumber46 startedwith a perfectlyclearearthup/down
rotationexplanationand changedto a sun up/down explanationat the end
of the interview. Another type of inconsistentexplanationwasa combination of occlusionof the sun versussun up/down movement.The children
who wereplacedin explanationtype 15 (undetermined)did not provide a
mechanismfor the day/night cyclein their responses.
Examinationof Figure3 showsthat, aspredicted,most of the first grade
childrenexplainthe day/night cyclein termsof the up/down movementof
the sun and moon, while most of the fifth gradechildrenusea rotation of
the earthexplanation.
156
VOSNIADOU
AND
BREWER
The Movement of the Moon
Children’sideasaboutthemovementof the moon weredeterminedby looking at the patternof their responsesto the four moon movementquestions
which appearin the top row of Table5 Op.157).Eight categoriesof explanation typesfor moon movementresponseswereobtainedand thesearealso
shownin Table 5. Protocol examplesfor someof thesecategoriesappearin
Table 6 (p. 158).
Childrenwho saidthat the moon doesnot moveto all the relevantquestions (430, 43 1, and 432) wereplacedin explanationtype 1. In Question
30 somechildren said that the moon appearsto move becausethe earth
movesbut that it doesnot really move.Similarly, somechildrenmentioned,
in responseto Question31, that the moon appearsto movealong with you
when you go for a walk but that it doesnot really move. One child said
spontaneouslythat the moon stayswhereit is andthe reasonwhy you don’t
seeit during the day is becausecloudscoverit up. Question33, “Why does
the moon move?“, wasnot askedfor thesechildrenbecausethey said that
the moon doesnot move.Seeprotocol 1, Table6 for anexampleof this type
of response.
The childrenclassifiedin explanationtype 2 all saidthat the moon moves
in an up/down fashion,in responseto Questions30and 32. Someof these
children claimed that the moon movesin a “hydraulic” relation with the
movementof the sun,that is, the moon goesdownin themorning whenthe
sun goesup, and later, when the sun goesdown the moon goesup. Most
childrensaidthat the moon doesnot movealongwith you whenyou go for
a walk (431) althoughsome acknowledgedthat it may appearto do so.
Finally, all the childrenexplainedthe movementof the moon (433) in relation to the day/night cycle. Seeprotocol 2, Table 6 for an exampleof this
type of responsepattern.
A number of children said that the moon revolvesaround the earth in
responseto Questions30and 32, and that it doesnot movealongwith you,
althoughit may seemso, in responseto Question31. Thesechildrenwere
placedin explanationtype 4. Most of the explanationsof the revolution of
the moon in Question33, “Why doesthe moon move?” weregivenin terms
of the day/night cycle--” to makeit night.” An exampleprotocolis givenin
Table6 (protocol4). No gravity explanationsweregivenin this categoryas
they weregivenin the previousone. The absenceof the scientifictypesof
explanationsin this categorysuggests
that therevolutionof themoon around
the earthwasnot understoodin termsof the scientificmodelbut wasseenas
causallyimplicated in the day/night cycle.
Table 5 showsthe frequencyof moon movementresponsesasa function
of grade.Thereis a clearshift from seeingthe moon asmoving at first grade
to seeingit as stationaryat grades3 and 5. Thus, the movementquestion
givesa very interestingU-shapedfunction. The young childrentend to say
the moon doesmove, the ,olderchildren tend to saythat it doesnot move,
5
Yes
Up and
Yes, Up/down
(3, 0, 2=5)
Yes, movement
unspecified
(11, 3,4=18)
Yes, revolution
around
earth
(0, 4, 2=6)
Yes, mixed
(0, 0, l=l)
2.
3.
4.
5.
No
8. No, undetermined
(2, 2, 1=5)
in parentheses
third for Grade
No
No, mixed
(1, 2, 0=3)
7.
a n=68
b The numbers
Grade
3, and the
Yes
6. Yes, undetermined
(1, 2, 2=5)
Yes
moon
for
move?
Movement
give the frequency
5. The last number
5
and
it seems
to
it seems
to
for each grade.
across
grades.
Ambiguous
response
(e.g.,
the sun was following
us
when my mom and I were
going to see my grandpa)
No
No
No
No or Yes,
move
No or Yes, it seems
to
move but does not really
No or Yes,
move
No or Yes
No, it seems to move;
it
it does not really
move
move along
you go for
Questions
TABLE
Does the moon
with you when
a walk?
Q31
of the Moon
of explanation
type
gives the frequency
moves
and
as if it moves
the
or without
revolution
Down
eorth
it seem
Yes, with
mentioning
Yes
No
No-the
makes
1. No, with or without
explanation
(2, 7, 8=17)b
the
Q30
Does
Types
of Movement
Type
Explanation
goes
around
the
it
time
so
number
is the frequency
Ambiguous
response
(e.g.,
the moon is on another
planet during the daytime)
Yes
No
No
Yes-it
earth
Yes or No-because
moves some other
Yes-it
moves
up/down
or
No-it
moves
at dawn
the sun can get up to
make day
No
Q32
the
moon
for
know
know
not
move.
for
move?
1, the second
does
does.
night
know
Grade
I don’t
I don’t
I don’t
The moon
The earth
To make
I don’t know
To make day/night
Because
of the earth’s
aravitv
day/night
relevant
does
To make
Not
Q33
Why
of Grade”
move when
in your bed?
as a Function
Does the moon
you are asleep
Frequency
The first
Their
No,
(No.
with
1, Grade
or without
5)
explanation.
Examples
(No.
Yes,
you
with
earth.
are
you
in your bed?
C: Yes. It moves around
the earth.
E: Why does the moon move?
C: So that when the sun comes
up here
_
be night on the other half.
when
the
along
move?
3)
around
move
moon
the moon
the
32, Grade
revolution
you go for a walk?
C: No.
E: Does the moon move
E: Does
c: Yes.
E: Does
Josh
4.
it will
asleep
when
E: Does the moon move?
C: Yes. No cross that out. It doesn’t
move.
It’s you that’s moving.
And it looks like the
moon is moving.
It’s still while you’re
moving.
E: Does the moon move along with you when
you go for a walk?
c: No.
E: Does the moon move when you are asleep
in your bed?
C: No. It stays in the same place.
The earth moves.
Joshuo
1.
Protocol
Yes,
Questions
(No.
1)
TABLE 6
Investigating
44, Grade
up/down.
the
the
Movement
E: Does the moon move?
C: Only up and down.
E: Does the moon move along with you when
you go for a walk?
c: No.
E: Does the moon move when you’re
asleep
in
your bed?
C: No.
E: Why does the moon move?
C: Cause when the sun’s gonna come up it
gotta go down, when the sun goes down
it gotto come up.
Quinten
2.
from
Yes,
(No.
5)
unspecified
13, Grade
movement
Moon
E: Does the moon move?
C: Yes.
E: Does the moon move along with you when
you go for a walk?
c: No.
E: Does the moon move when you are osleep
in your bed?
C: Yes.
E: Why does the moon move?
C: Because
it’s attracted
to the earth’s
gravity.
And it moves
with the earth.
Luther
3.
of the
DAY/NIGHT
CYCLE
159
andadultssayit doesmove(unpublisheddatafrom undergraduate
subjects).
Cur detailedcategorizationof the different typesof moon movementprovidesa very goodexplanationfor the progressionof thesedifferent answers
to thesameverbalquestionwith age.Whenthe youngsubjectssaythemoon
movesthey tend to meanthat it movesin an up/down fashionwith respect
to the earth’ssurface. When the older subjectssay that it doesnot move
theyaretypically operatingwith a rotating earthmodelwith themoon fixed
in oneposition.Whenadult subjectssaythe moon movestheyarereflecting
thescientificmodel in which themoon revolvesaroundthe earth,This analysisof responsesto questionsabout the movementof the moon showsthe
powerof the mental model approachin providing an explanationof data
that, at first glance,appearquite puzzling.
The Disappearance of the Stars During the Day
Children’sexplanationsof the disappearanceof the stars during the day
wereexploredby askingthe threequestionswhich appearin the top row of
Table7 (p. 160).The various explanationtypesand their frequenciesare
shownin Table7. Protocol examplesfrom eachcategoryareshownin Table
8 (p. 161).The data presentedin Table 7 showthat the first-gradechildren
givea wide rangeof explanationsof the disappearance
of the starsduring
theday-they are occludedby cloudsduring,theday, they move down on
theground,they move to the other sideof the earth. Theseare similar to
their explanationsof the disappearanceof the sun at night. However,the
largestgroup of children (24 out of 60) said that the starsstay wherethey
areduringthe day andthat the reasonwe cannotseethem is becauseof the
brightnessof the sky dueto the light comingfrom the sun.This explanation
is particularlycommon among the fifth-grade children(12 out of 20).
Overall Mental Models of the Day/Night
Cycle
Childrenwereplacedin the variousexplanationtypesalreadydiscussedif
theymet the criteria for logical consistencywhich we developedon a priori
basisand which werepreviouslydescribed.In this sectionwe describethe
criteriausedto assignchildrento an “overall mentalmodel of the day/night
cycle.” In orderto be assignedto an overallmodel of the day/night cyclea
givenchild had to havebeenplacedin explanationcategoriesin the four sets
of questionspreviouslydiscussedwhich werenot logically inconsistentwith
eachother.
Thecriteriafor assigningchildrento mentalmodelsaredescribedin Table
9 (PP.162-163)and arediscussedin detail in the following sectionaccording to model numbers.The frequencyof occurrenceof eachmodel type by
gradeis also givenin Table 9.
Model I: The Sun is Occluded. The four childrenplacedin this category
all saidthat something(usuallycloudsor darkness)blocksthesun,in response
The stars
the earth
move down,
(3, 1, 1=5)
ore
a n=tJl
b The numbers
Grade
3. and the
9. Undetermined
(4, 3, 2=9)
in parentheses
third for Grade
sky
sky
sky
sky
sky
sky
sky
sky
sky
ore
During
of explanation
type
aives the freauencv
at night?
of the Stars
the stars
give the frequency
5. The lost number
In the
In the
where
they
In the
In the
8. The stars stay
(3, 9, 12=24)
somewhere
of
In the
In the
The stars move
else (l,O,O=l)
side
under
In the
In the
In the
Where
Q36a
the Disappearance
7. The stars dtsoppear
(l,O,
O=l)
6.
5. The stars move down,
unspecified
as to which
earth (2, 0, 0=2)
4.
the
3. The stars go down on/in
ground
(behind
hills)
(1, 0, 1=2)
for
space
out
2. The stars move
(2, 2, 1=5)
by
Types
into
occluded
of Explanation
1. The stars are
clouds
(3, 5,3=ll)b
Type
Explanation
7
hills
Behind
for each grade.
across
arades.
The first
No response,
I do not
irrelevant
or ambiguous
number
stars
they
for
Grade
1, the second
move
move?
of Grade”
don’t
know
Yes or No
No,
I don’t
Yes
Yes
Yes
Yes
Yes
Yes or No
Do the
Q37
as a Function
is the frequency
know,
response
are still up on the sky. You
see them because
of the
light
f.
They
can’t
sun’s
gone-disappeor
country
side
are
city,
go down
or the
space
Frequency
the day?
other
Their
during
and
They
Another
They
They go under
of the earth
owoy,
into
they
Clouds
are
Questions
Move
Behind
.Where
Q36b
the Day
TABLE
for
Autumn (No. 51, Grade 1)
E: Where are the sto” at night?
c: In the sky.
E: In the day?
c: Into another city.
E: Do the stars move?
c: Yes.
else.
Rusrel (No. 59. Grade 1)
E: Where are the stars at night?
c: They an In the sky.
E: During the day?
c: In the day they are gone.
Disappear
E: Do the rtws move?
c: I don’t know.
7. The stars dInappear.
h?
c: wuy in space and when it gets
daytime they go down.
E: Do the .ten move?
c Yes
d4
c: Behind the clouds.
E: Do the stars move?
t: Yes.
6. The stars move somewhere
Margaret (No. 60, Grade 1)
E: Where ore the stars ot night?
C: Up In the sky.
E: Where ora the stars during the
Sandy (No. 57. Grade 1)
E: Where ore the stars at night?
c: In the sky.
E: Where ore they during the
move Od into space.
2. The ,tan
1. The stws are occluded by clouds.
E: Where are the ston during the
day?
c: Thy am still in space.
E: Can we roe them?
c: No.
E:why?
c: Seause we’re facing the sun and
the sun gives us too much light
and we can’t we them.
E: Do the stars move?
c: No.
c: They 010 In q&a.
Donlelle (No. 4, Grade 5)
E: Where ore the $an ot night?
8. The stat-a stw where thev ore
Betsy (No. 53. Grade 1)
E: Where 0” the stoe at night?
c: .ln tfw sky.
E: Where ore the stars during the
day?
c: Down behind the hills.
E: Do the stars move?
c: Only when it is doytlme.
of the Stan
c:
E:
C.
E:
c:
E:
c:
day?
They are not there.
When are they?
I don’t know.
Do the stars move?
Yes.
How.
Once In D while they move with
you when you walk or ride a
bike or when riding a car
hvln (No. 55. Grade 1)
E: Where are the stars ot night’?
c: In space.
E: Where are the stars during the
9. Undetermined.
Brian (No. 43. Grade 3)
E Where are the stars ot night?
.c: Up in the sky.
E: Where ore the stoo during the
day?
c: Under the earth.
E: How did this hopp+n?
c: When the sun comer out the stars
go down and the moon goes
dam.
E: Do the stoo move?
c: Ya¶
4. The stars move down under the
earth.
TABLE 8
Investigating the Dlsappearonce
3. The stars move dawn on/in the
ground.
Protocol Examples from the Questions
Donald (No. 49, Grade 1)
E: Where are the stars ot night?
c. up In the sky.
E: Where am the stars during the
day?
c: Down hers. They went down.
E: Down where?
c: Down some place.
E Do the stars move?
c:Ye,
-Ills stms move down, unspecified as
as to which side of the earth.
Sun revolves
earth
Earth revolves
the sun
Earth
fixed
6. Sun and moon revolve
around
earth every day
(0, 1, O=l)
7. Earth and moon
revolve
around
the sun
every
day (0, 1, O= 1)
8. Earth rotates
up/down;
sun and moon fixed at
opposite
sides
(1,3,7=11)
turns
Sun moves
space
5. Sun moves out into
space (1, 1,0=2)
sun
around
around
and
out
into
Sun moves
unspecified
4. Sun and moon move
up/down
unspecified
(3, 0, 0=3)
down
Sun moves
down to
the other side of the
earth
on
is
of
9
and
Their
Frequency
around
Earth turns in
up/down
direection
Earth revolves
sun and moon
into
moon
around
out
down
and
Sun revolves
earth
Sun moves
space
Sun goes
unspecified
goes up
Sun goes down to the
other side of the
earth and moon goes up
Sun goes down on the
ground
and moon
goes up
Sun is occluded
by
clouds or darkness
of the
Cycle
TABLE
Cycle
Explanations
Day/Night
of the Day/Night
3. Sun and moon move
up/down
to the other
side of the earth
(2, 0, 0=2)
down
Sun is occluded
clouds or darkness
The Disappearance
the Sun &restions
Models
Sun moves
the ground
Sun is occluded
by
clouds or darkness
(2.
..- 1. 1=4P .
of Model
Mental
2. Sun and Moon move
up/down
on the
ground
(7, 0, 0=7)
I.
Type
Overall
Moon
Moon
Moon
earth
Moon
does
moves
revolves
moves
Moon moves
unspecified
Moon moves
unspecified
Moon moves
unspecified
not
move
unspecified
around
unspecified
up/down
up/down
up/down
or
or
or
of Grade”
Moon moves
unspecified
or does not move
The Movement
of the Moon
as a Function
of
are occluded
or
behind
clouds
the
move
stay
stay
where
where
Stars stay where
move into space,
occluded
Stars
Stars
out
are
are
Day
(continued)
they ore,
or are
they
they
into
unspecified
go down to the
side of the earth
Stars move
space
Stars
Stars
other
Stars disappear-occluded
by clouds
or hills--move
into space
Stars
move
The Disappearance
the Stars During
Mixed:
Earth rotates
sun moves
up/down
fl. 0.4=51
13.
Undetermined
(1, 2, 0=3)
16.
rotates
(1, 2, 2=5)
turns
and
sun
turns
unspecified
rotates
Undetermined
or
God made it that wav
Mixed:
sun occluded
moves
up/down
and
earth rotates
Mixed:
earth
and revolves
Mixed:
earth rototes
sun moves
up/down
Earth
Earth turns around
axis and sun is fixed
Earth turns around
axis or unspecified
Earth
fixed
and
and
is
turns
turns
turns
unspecified
around
around
in up/down
rototes
and
The first
Undetermined
or
God made it that wav
Mixed
Mixed:
earth
and revolves
Mixed:
earth rotates
sun moves
up/down
.
Earth
Earth
axis
Earth
axis
Earth turns
direction
9 (Continued)
b The numbers
in parentheses
give frequency
of explanation
type for each grade.
3, and the third for Grade
5. The last number
gives the frequency
across
grades.
Mixed:
generol
(0, 5, 1=6)
15.
14. Mixed:
earth
ond revolves
Earth rotates
in
unspecified
direction
(1, 1, 1=3)
12.
and
Earth rotates
around
axis; sun is fixed but
moon moves
(0, 1, O= 1)
11.
rotates
around
sun and moon
at opposite
sides
1=2)
Earth
axis:
fixes
(0, 1,
10.
9. Earth rotates
up/down;
sun is fixed but moon
moves
(0. 1, 3=4)
TABLE
does
not
move
number
Moon
move
Moon
move
Moon
move
The
Move
move
or does
or does
or does
is the frequency
moves
moves
not
where
where
occluded
where
1, the second
Anything
Anything
Anything
Anything
stoy
stay
Stars
Stars
are
stay
Stars
Stars
for Grade
not
not
not
or mixed
or does
moves
moves
moon
moves
Moon moves
unspecified
or revolves
around
earth
Moon
Moon moves
unspecified
or revolves
around
earth
for
are
are
ore
Grade
they
they
they
164
VQSNIADOU
AND
BREWER
to the questionsregardingthe disappearance
of the sunduringthe night and
in the questionsrequiring an explanationof the day/night cycle. Two of
thesechildrensaidthat somethingalsoblocksthe moon andthe starsduring
the day, but the remainingtwo said that the moon and the starsmove in
an unspecifiedway or move in order to go behindthe clouds which then
coverthem.
Wedistinguisheda classof mentalmodels(Models2 to 6) which arebased
on the assumptionthat the alternationof day andnight happensbecausethe
sun and the moon move up/down and exchangepositions. Thesemodels
were further differentiatedwith respectto exactly wherethe sun and the
moon move:Model 2: on the ground; Model 3: to the other side of the earth;
Model 4: unspecified; Model 5: out in space; and Model 6: revolve around
the earth.
Model 2: The Sun and the Moon Move Up/Down on the Ground. The
sevenchildrenplacedin Mental Model 2 all said that the sun movesdown
on the ground,in responseto the questionsregardingthe disappearance
of
the sun; that the moon movesup/down or unspecified,in responseto the
questionsregardingthe movementof the moon; that the day/night alternation occursbecausethe sungoesdown with additionalpossiblereferenceto
the moon goingup, in responseto the questionsregardingthe explanation
of theday/nightcycle;andthat thestarsdisappearin variousways-undetermined, occludedby cloudsor hills, or move into space,in responseto the
questionsregardingthe disappearanceof the starsduring the day.
Model 3: The Sun and the Moon Move Up/Down to the Other Side of
the Earth. Two childrenwereplacedin this mental model. They both said
that the sun movesup/down to the other sideof the earth, that the moon
movesup/down or unspecified,that the day/night cyclehappensbecause
the sun movesdown to the other sideof the earthand the moon movesup,
and that the starsalso moveto the other sideof the earth during the day.
Model 4: The Sk and the Moon Move Up/Down But Unspecifiedwith
Respectto EarthZide. The threechildrenplacedin this categoryall saidthat
the sun and moon move up/down but differed from the childrenplacedin
the previouscategoryin that they did not giveinformation asto whetherthe
sun movesdown on the ground or to the other sideof the earth.
Model 5: TheSun Moves Out in Space.Two childrenwereplacedin this
category.They both saidthat the sunmovesout into spaceduring the night
and that the samehappensto the starsduring the day. Thesechildrenalso
explainedthe day/night cyclein termsof the sun’smovementinto spaceand
said that the moon movesin responseto the moon,movementquestions.
DAY/NIGHT
CYCLE
165
Model 6: The Sun and the Moon Revolve Around the Earth Every Day.
Only onechild wasplacedin this interestingmodelin which the sunandthe
moon (at oppositesides)revolvearoundthe eartheveryday: Whenthe sun
is on our sideof the earth,the moon is on the other side.Accordingto this
modelthe starsremainwherethey areduringthe dayandthereasonwe cannot seethem is becauseof the brightnessof the sun’slight.
We identified six different mental models (Models7 to 12),which used
the movementof the earth as the basisfor forming an explanationof the
day/night cycle. Thesemental modelswere differentiatedwith respectto
thetypeof movementof the earth(e.g.,Table9, revolution- Model 7; rotation - Models8, 9, 10, 11and 12).The rotation modelswerefurther differentiatedwith respectto the type of rotation (up/down or west/east)aswell
as with respectto the movementof the moon (moon fixed or revolving
aroundthe earth).
Model 7: The Earth and the Moon Revolve Around the Sun Every Day.
Only onesubjectwasfound to haveformed Model 7 accordingto whichthe
earthand the moon revolvearound the sun every24 hours, and the stars
staywherethey are.
Model 8: The Earth Rotates Up/Down; the Suri and the Moon are Fixed
at Opposite Sides. The 11childrenwho wereplacedin this classificationall
explainedthe disappearanceof the sun at night by sayingthat the earth
turnsandthat the sunis fixed. Thesechildrenalso saidthat the moon does
not movein responseto the questionsregardingthe movementof the moon.
The day/night cyclewasexplainedin terms of the up/down rotation of the
earth.They gavea variety of explanationsof the stars(e.g., the starsstay
wherethey areand we cannotseethem becauseof the sun’slight, they are
occludedby cloudsor move out in spaceduring the day).
Model 9: Earth Rotates Up/Down;
the Sun 13Mxed But the Moon Moves.
This mental model is similar to the previousone with only one exception.
Themoon is not fixed at the oppositesideof the earthfrom wherethe sunis
locatedbut moveseitherin an unspecifiedway or revolvesaroundthe earth.
Four childrenwereplacedin this category.
Model 10: Earth Rotates Around Axis; the Sun and the Moon are FLved
at Opposite Sides. Two children wereplacedin this category.They both
saidor indicatedin their drawingsthat the earth turns aroundits (north/
south)axisin responseto the questionsregardingthe disappearance
of the
sunat night and/or the questionsrequiringan explanationof the day/night
cycle.In addition,they saidthat the moon doesnot moveandthat the stars,
which also do not move, are occludedby cloudsduring the day.
166
VOSNIADOU
AND
BREWER
Model II: Earth Turns Around Axis; the Sun 2s Fiked, But the Moon
Moves. Only one child wasidentified as havingthis model. This child said
that the earth turns around its axis, the sun is fixed, the moon revolves
around the earth, and the starsstay wherethey are.
Model 12: Earth Turns in Unspecified Direction; Sun is Fked But Moon
May or May Not Move. The childrenplacedin this categorydid not specify
how the earthmoves.Someof thesechildrensaidthat the moon movesand
othersthought it is stationary.Threechildren wereplacedin this model.
A numberof mixedmentalmodelsof the day/night cyclewereidentified.
Wedifferentiatedthemodelswhichpresenteda combinationof earthrotation
and sunmovesup/down explanations(Model 13)from thosewhichconfused
rotation andrevolution(Model 14).All otherswereplacedin a generalmixed
model. The childrenwho did not provide enoughinformation to be placed
in a mental model wereput in the undeterminedcategory.
Model 13: Mixed. Earth Rotates and Sun Moves Up/Down. The five
children placedin this model thought that the earth rotates and the sun
movesup/down at the sametime. Most of thesechildrenthought that the
moon also movesand provided different kinds of explanationsregarding
the disappearance
of the starsat night (e.g.,staywheretheyare,movedown,
are occluded).
Model 14: Mixed. Earth Rotates and Revolves. Another five children
explainedthe day/night cyclesometimesin termsof the earth’srotation and
sometimesin terms of its revolutionarymovement.
Model 15: Mixed General. This categoryincludedvariousmixed explanations of the day/night cycle. Somechildrenattributed the day/night cycle
both to the occlusionof the sun by cloudsand its movementdown to the
ground.Somechildrenmentionedin additionto thesetwo explanationsthat
the earthrotatesor revolves.Onechild first gavean explanationof the day/
night cyclein termsof the up/down movementof thesunandthe moon and
lateran explanationin termsof therevolutionof thesunandthemoon around
the earth. Six children wereplacedin this category.
Model 16: Undetermined. The threechildrenin this categorygaveundetermined responsesto the questionsregardingthe disappearanceof the sun
during the day and the questionsrequiringan explanationof the day/night
cycle, or said that “God madeit that way” in one of them.
The frequencyof the mental modelsof the day/night cycleasa function
of gradeis shownin Table 9. We againseea shift from an initial model of
an up/down moving sun and moon to earth rotation explanationswith
increasinggrade.
DAY/NIGHT
of the
Subiect
TABLE 10
Relationship
Between
Children’s
Day/Night
Cycle and their Models
Model
NO.
No.
167
Overall
Models
of the Shape of the
Eartha
& Description
Earth
RecfoflgulOr
4. Sun and
49
Duo1 Earth
42, 51
53, 57, 59
moon
move
up/down
unspecified
1. Sun is occluded
by clouds or darkness
2. Sun and Moon move up/down
on the ground
5. Sun moves
out into space
31, 52
Hollow
9
2
CYCLE
Sphere
1. Sun is occluded
by clouds or dorkness
8. Earth rotates
up/down:
sun ond moon fixed at opposite
sides
9. Earth rotates
up/down;
sun is fixed but moon moves
10. Earth rotates
around
axis: sun and moon fixed at opposite
13
20, 33
Flattened
43
Sphere
3. Sun and moon move
11. Earth rotates
around
11
Sphere
24
1. Sun is occluded
39
7. Earth
B. Earth
sides
9. Earth
1, 3, 4, 7, 18,
19, 26, 20, 29, 50
5, 6, 36
a Only
sides.
subjects
who
hove
well
up/down
to the other side of the
axis: sun fixed but moon moves
by clouds
or darkness
and moon revolve
rotates
up/down;
around
the sun every
doy
sun and moon fixed at opposite
rotates
sun
up/down:
specified
models
earth
is fixed
of both
earth
but
moon
shape
moves
and day/night.
Relationship Between Children’s Overall Mental Models
of the Day/Night Cycle and Mental Models of the Earth
In theintroductionwe describedsomeof the constraintsthat mentalmodels
of the earthimposeon mentalmodelsof the day/night cycle(seeFigure2).
Sincewe had independentlyassignedthe children who participatedin this
studyto mentalmodelsof the earth(seeVosniadou8cBrewer,1992),wehad
theinformation requiredto examinethe relationshipbetweentheir mental
modelsof the day/night cycleand their modelsof the earth. As Table 10
shows,this comparisonindicatedthat the childrenwith rectangle,disc,and
dual earthmodelsprovidedexplanationsof the day/night cyclein termsof
the up/down movementor occlusionof the sun (Models 1, 2, 4, or 5), or
hadmixed or undeterminedmodels.
We did not observeany caseswherea fundamentallyflat model of the
earthwasassociatedwith an explanationof the day/night cyclein termsof
therevolutionor rotation of the earth,or eventhe explanationaccordingto
whichthe sun goesdown to the other sideof the earth(Table9, Model 3).
168
VOSNIADOU
AND
BREWER
On the other hand, childrenwith sphericalor syntheticmodelsof the earth
typically gaverotational explanationsand only occasionallygaveexplanations of the day/night cyclein termsof occlusionor of the up/down movement of the sun and the moon. We carried out an analysisof the data
presentedin Table 10.The childrenwho held flat modelsof the earthwere
comparedwith the overall sampleof children with specifiedearth models
with respectto the numberwho held “no rotation” models(Models1,2,4,
& 5) versusother models of the day/night. The children with flat earth
modelswerereliablydifferentfrom the overallsample,x2(1, N = 8)= 16.00,
pc .OOl.Theseresultsare consistentwith our predictionsthat the mental
model of a sphericalearthsurroundedby spaceis a necessary,but not sufficient, condition for the acquisition of the scientific explanation of the
day/night cycle.
DISCUSSION
Mental Models of the Day/Night
Cycle
The resultsof the presentstudyshowedthat 38out of the 60 childrenin our
samplecouldbeassignedto a coherentmentalmodelof the day/night cycle.
A graphicrepresentationof the subsetof modelsthat the children in our
sample constructed(not including undeterminedor mixed models), is
presentedin Figure 5.
The mentalmodelsof the day/night cyclewhichwe obtainedweresimilar
to the explanationsidentified in previous research(e.g., Baxter, 1989;
Sadler,1987).The childrenprovidedaccountsof the alternationof day and
night in terms of the sun going down behindthe hills or beingcoveredby
clouds,or they gaveexplanationsbasedon the notion that the sunrevolves
aroundthe earthor that the earthrevolvesaroundthe sunor rotatesaround
its axis. There was one explanationidentified by Sadler and by Baxter
(accordingto which the moon blocks the sunat night) which wasnot identified in the presentsample,but which has appearedin someof our text
comprehensionstudies(seeVosniadou,1991b).
Therewasalsonoticeablesimilarity betweenchildren’smentalmodelsof
the day/night cycle and the kinds of explanationsof the day/night cycle
found in the history of astronomy.Like the early astronomers,the young
children in our sample explainedthe day/night cyclein terms of the sun
moving to distant parts of the earth, hiding behind hills or mountains,or
setting.underthe earthin the westto rise in the east.
Three Kinds of Mental Models: Initial, Synthetic and Scientific
Our theoreticalframeworkled us to predictthat we would find threekinds
of mentalmodelsof the day/night cycle:(a) initial models-models consistent with the observationsbased on everydayexperience;(b) synthetic
models-representingattemptsto reconcilethe culturally accepted,scientific
DAY/NIGHT CYCLE
The sun is occluded by
clouds or darkness.
4.
169
The sun moves out into
space.
The sun and the moon move
up/down on the ground.
0
*
DT
0
The sun and the moon revolve
around the earth once every day
The sun and the moon
move up/down to the
other side of the earth.
7.
6.
c
(a) or
(b)
The earth rotates up/down or
west/east. Sun and moon are
fixed at opposite sides.
The earth and the
moon revolve around
the sun every 24 hours.
The earth rotates
west/east. Sun is fixed
but moon revolves
around earth.
Figure
5. Mental models of the day/night
cycle.
explanationof the day/night cyclewith observationsbasedon experience;
and(c) scientific models-models which agreewith the scientific view. The
mentalmodelsof the day/night cyclewe obtainedin this studycan indeed
be groupedin thesecategories.
We considerthe modelswhich assumethat the earth is stationaryand
that the sun is occludedby something,movesin an up/down direction, or
movesfar away(Models 1,2, and3 in Figure5) to be clearexamplesof initial models. Thesemodels do not show any influencefrom the culturally
acceptedview in which the alternationof day/night is causedby the earth’s
170
VOSNIADOU
AND
BREWER
axis rotation, nor do they includeany other information which reflectsexposureto other aspectsof scientific information, suchas, for example,information regardingthe sphericalshapeof the earthor therevolution of the
eartharoundthe sun.Thirteenout of the20first-gradechildrenin our sample
providedinitial modelsof the day/night cycle, while only two third-grade
childrenandonefifth-gradechild adoptedaninitial model.Analysisof these
data showsthat among the first-gradechildren there were reliably more
childrenwith initial modelsthan with syntheticmodels,x2 (1, N= 16)= 6.25,
p< .02.
Syntheticmodelsrepresentattemptsto assimilatescientificinformation
to an existinginitial model. The obtainedsyntheticmodels(Models4,5,6,
and 7 in Figure 5) differed from the scientific explanationalong three
dimensions:what movesto producethe day/night cycle,how theseobjects
move, and whetherthe moon is causallyimplicatedin the day/night cycle.
As we have seen, some children think that the day/night cycle results
becausethe sun and the moon revolve around the earth, or becausethe
earth revolvesarounda stationarysun. Older children think that the earth
rotatesup/down and that the sun and moon are fixed at oppositesides.A
number,,of the third-grade children and a majority of the fifth-grade
children in our sampleprovided syntheticmodels of the day/night cycle
(grade1: 3/20; grade3: 7/20; grade5: 11/20).Analysis of thesedata show
that amongthe fifth-grade children therewerereliably more childrenwith
syntheticmodelsthan with initial models, x2 = (1, N= 12)=8.33, pc .Ol.
The model which comesclosestto the culturally-acceptedscientific explanationis Model 8 (Figure5), which includesa fixed sun,axisrotation of
the earth, and revolution of the moon aroundthe earth. Only one child, a
third grader,formed this model.
The remaining22childreneitherdid not havecoherentmodelsor did not
provideenoughdatafor usto understandtheir models.Threechildrengave
models.inwhichthe directionof the earth’srotation wasunspecified(Model
12, Table 9), while threeadditional children were placedin a categoryin
which the day/night model wascompletelyundetermined(Model 16,Table
9). Finally, 16childrenwereplacedin a mixed modelcategory.Five of them
usedboth the up/down movementof the sunand the rotation of the earth
to explainthe day/night cycle(Model 13,Table 9). Another five usedboth
the earth’srevolutionaroundthe sunandthe earth’srotation to explainthe
day/night cycle (Model 14, Table 9). The six remaining children useda
variety of mechanismsin their explanations(Model 15, Table9).
Age Trends in Mental Model Construction
Although the presentstudy was cross-sectionaland not longitudinal, the
results clearly show that the majority of first-gradechildren enter school
having formed an initial model of the day/night cycle. During the elementary school yearsthey appearto replacethe initial model with a synthetic
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model. By the end of their elementaryschool years,some children have
replacedtheir syntheticmodel with the scientific model.
It is interestingto note that the likelihood of children’smodelsbeinginconsistentincreasesafter the first grade.This finding is in agreementwith
the hypothesisthat the mixed modelsare a product of children’sfailed attemptsto reconciletheir initial modelswith the culturally acceptedmodel
ratherthan someoverall inability to form coherentmodels.
Constraints on Children’s Mental Models of the
Day/Night
Cycle
In the Introductionwe discussedhow mental modelsof the day/night cycle
areconstrainedby a hierarchyof constraints(presuppositions,beliefs,and
mentalmodelsof the earthandthesun).Theseconstraintsweredescribedin
the hypothetical knowledgeacquisition processshown in Figure 1. The
mental models we have obtainedin this study are in agreementwith this
hypothesizedconceptualstructure.
Presuppositions
Thehypothesisthat certainontologicalandepistemologicalpresuppositions
constrainchildren’s mental models was confirmed. The resultssuggested
that the childrenhonoredseveralepistemologicalpresuppositions.All the
children were capableof understandingth,at the alternation of day and
night constitutesa phenomenonthat requiresan explanation.In addition,
almostall of the children in our sampleprovided mechanistic/causalexplanationsof this phenomenon.Only one child said that “God makesit
happens,”and noneof the children in this samplegaveanimistic explanations. It should be noted that the scientific explanationof the day/night
cycledoesnot requirethe revisionof theseepistemologicalpresuppositions.
It does,however,requirethe revisionof someontologicalpresuppositions
which influencechildren’smental models of the day/night cycleindirectly
through their mental models of the earth. Theseconstraintswill be discussedin the sectiontitled “Mental Models of the Earth.”
Beliefs
Our resultsshowedthat most childreninferredfrom their observationsthat
theday/night cycleis causallyrelatedto the appearanceand disappearance
of boththe sunandthe moon. The erroneousbeliefthat themoon is causally
implicatedin the day/night cycle appearedto be presentin the synthetic
modelsof the oldestchildrenin our sample.It is not clearwhy this belief is
sopersistent.It couldberelatedto the fact that in the usualpresentationsof
thescientificexplanationof the day/night cyclethe role of the moon is not
usuallyclarified. In an investigationof theastronomyunits on the day/night
cyclein four widely-usedscienceseriesfor elementaryschoolstudents,we
did not find any discussionof the role of the moon in the day/night cycle
(Vosniadou,1991a,1991b).
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The mechanismusedto explainthe appearanceand disappearance
of the
sun and the moon relied either on the notion that their movementtakes
themsomewherewherethey cannotbe seen,or on the notion that something
comesand occludesthem. We did not obtain any switch on/off explanations. The mechanismaccordingto which the viewerturns (or, rather, that
the earth turns) so the viewer cannot seethe object anymoreseemsto be
availablebut is not applieduntil the childrencanconceptualizethe earthas
rotating or revolving. As we havealreadyseen,this doesnot happenuntil
the children form the model of an earthsurroundedby space,eventhough
this model may not be the scientific model of a sphericalearth with people
living all aroundit on the outside.
Mental Models of the Earth
Someof the most interestingfindings of the presentstudy haveto do with
the constraints that mental models of the earth impose on the mental
modelsof the day/night cycle.Mental modelsof the earthinfluencemental
models of the day/night cyclein two ways:
Fist, considerthe flat earthversussphericalearthdistinction. Flat earth
modelsare constrainedby the presuppositionsthat the ground is flat and
that unsupportedthingsfall (cf. Vosniadou& Brewer,1992).In Figure2 we
describedhow thesepresuppositionsand the flat earth modelsthey entail
constrain children’s mental models of the day/night cycle. Our results
showedthat theseconstraintswere,in fact, observed.All the childrenin our
samplewith a flat earthmentalmodelformedinitial modelsof the day/night
cycle(seeTable 10).
In addition to the flat vs. sphericalearth distinction, there were other
aspectsof children’s specificmental modelsof the earth that appearedto
imposeconstraintson how they explainedthe day/night cycle.An example
of this canbefound in children’salternativeinterpretationsof the up/down
movementof the sun dependingon their particular mental model of the
earthas shownin Figure 3, explanationtype 4.
We alsofound that childrenwith hollow spheremental modelshaddifficulty comingup with a coherentmodel of the day/night cycle.Sevenof the
12childrenwith hollow spheremodelsgaveunspecified,mixed, or undetermined,day/night cycle explanations.There wereonly two examplesof an
up/down rotation mental model of the day/night cycle, a finding which is
consistentwith the hypothesisthat these children have constructed
the
.__
hollow spheremodel underthe constraintsof an up/doGgravity presupposition. Obviously,the up/down rotation of the earthis not a very viable
solution for thesechildren. A better solution of the day/night problem,
givena hollow spheremodel of the earth, is to assumea west/eastrotation
of the earth, which doesnot violate the up/down gravity presupposition.’
Two childrenwith hollow spheremodelsselectedthis solution. The mental
model of a west/eastrotating hollow sphereis also a problem for children
DAY/NIGHT
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with hollow spheremodels,however,becauseit doesnot easilyexplainthe
disappearance of the sunat night. In orderto makethesundisappear
at night
somechildrencreatea “day side” of the earth and a “night side” of the
earth,Giventhis model, the sundisappearsfrom our sightwhenwe moveto
the “night side” of the earth, as the earth rotatesfrom west to east(see
drawingnumber 12, Figure 4, and explanationtype 12,Table 4).
Anotherinterestingempiricalrelationshipexistsbetweenthe directionof
theearth’srotation and children’searthshapeand day/night cyclemodels.
Therewereonly threechildrenwho formed west/eastrotation modelsof the
earth.Two of them had a hollow sphereearth model and one a flattened
sphereearth model. On the other hand, there were 23 children with
sphericalearth models, 13 of whom attributed the day/night cycleto the
rotational movementof the earth. All of these13 children conceptualized
the earthasrotating in an up/down direction(i.e., rotation aroundan axis
throughthe equator).There are a number of possibleexplanationsof the
preferencesphericalearth children show for an up/down rotation of the
earth.One explanationis basedon the similaritiesthat exist in the model
of a rotatingearthanda fixed sun(model7a, Figure5), and the model of a
stationaryearthand anup/down movingsunandmoon (seemodel4, Figure
5). The two models are identical with the exception that in one the
day/night cycle is explainedin terms of the rotational movementof the
earth(up/down rotation) whereasin the otherit is explainedin termsof the
up/down linear movementof the sun and the moon. It appearsthat childrenwith a sphericalearthmodelwho haveformed modelnumber4 (Figure
5)may tendto moveto model 7a, whenthey aretold that the reasonfor the
disappearance
of the sun is the rotational movementof the earth.
Model 7a (Figure 5) is also consistentwith the belief that the sun is
locatedabovethe top of the sphericalearth,ratherthan in the planeof the
earth’sequator.Sucha belief may be a remnantof an initial model of the
day/night cycle,basedon everydayexperience,which children continueto
hold evenwhenthey haveunderstoodthat the shapeof the earthis spherical. Givensucha belief, the creationof a model of the day/night cyclewith
explanatoryadequacyrequiresan up/down rotation of the earth, so that
thepersonlocatedon the top part of the earth, facingthe sun,will be away
from the sun when it is night. Our analysesof the direction of the earth’s
rotation suggestthat the up/down rotation of the earth is a rather subtle
form of syntheticmodel construction.
To conclude,the resultsof the presentstudyconfirm our originalhypothesisthat children’s mental models are influencedby a hierarchyof constraints,which we havecalledpresuppositions,beliefs,and mentalmodels,
that operatesimultaneouslyon the knowledgeacquisitionprocess.Someof
theseconstraints(e.g., the ontologicalpresuppositionswe haveidentified,
thebelief that the sun moves,etc.), operatein a similar fashionin the case
of childrenwho grow up in different cultures(seeVosniadou,in press-b),as
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well as in the early astronomerswho tried to explain the day/night cycle,
The latter finding supportsa limited form of recapitulation(cf. Brewer&
Samarapungavan,1991)to the extentthat someof the presuppositionsand
beliefsconstrainingthe constructionof mentalmodelsin childrenandearly
astronomersaresimilar.
Explanations of the Construction
of Synthetic Models of the Day/Night Cycle
In our previouswork (Vosniadou& Brewer, 1992)we explainedthe formation of syntheticmodelsof the earthasthe productsof the graduallifting of
the constraintswhich operateon initial modelsof the earthunderthe influenceof the information providedby the culture. The resultsof the present
investigationshowthat this analysiscanalso explainthe formation of synthetic modelsof the day/night cycle.
For easeof expositionwe will basethis discussionon the subsetof day/
night models presentedin Figure 5. The three initial day/night models
(Models 1, 2, 3) are constrainedby the initial earth shapemodel of a flat
andstationaryearth. In thesemodelsthe day/night cycleis producedeither
by the up/down movementof the sun (moon) to the earth’ssurfaceor by
the occlusionof the sun (moon).
The first fundamentalchangewhich allows the formation of synthetic
modelsof the day/night cyclerequiresthe lifting of the constraintimposed
by the model of a flat earth, and, therefore,indirectly, of the constraints
imposedby the ontologicalpresuppositionsthat the groundis flat andthat
unsupportedobjectsfall in a downwarddirection.By adoptingthe modelof
a sphericalearthasan object (motionless)in spacechildrencan explainthe
day/night cycleby havingthe sun (moon) go down to the other sideof the
earth (Model 4).
Acceptingthe model of a sphericalearth surroundedby spaceallows a
number of additional syntheticday/night models.The children who hold
Model 5 believethat the sun and moon revolvearoundthe earthevery24
hours. This model is similar to Model 4 exceptthat the postulatedmovement of the solarobjectsis revolutionratherthan up/down. It seemslikely
that the children holding Model 5 have been influencedby information
from the culture about the revolution of the moon aroundthe earth or of
the eartharoundthe sunwhich they haveusedto generatea classicgeocentric model of the day/night cycle.
The childrenwith Model 6 havegiven up the belief that the earth does
not move. Thesechildren believethat the earth revolvesaround the sun
every24hours. Note that if oneassumesthat the earthdoesnot revolveon
its axis, then this model providesan explanatoryaccountof the day/night
cycle.Nevertheless,we think it is unlikely that elementaryschoolchildren
havearticulatedtheir modelswell enoughto understandthis point andthat
it is more likely that most of thesechildren haveassimilatedinformation
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about the earth’s yearly revolution around the sun into their day/night
model without developing a completely specified model.
The children with Model 7 have also given up the constraint that the
earth is motionless but use the earth’s rotation (either up/down or
west/east) to explain the day/night cycle. This model begins to converge on
the scientific model but still contains an important synthetic component.
The children with this model assume that the sun and moon are fixed in
space at opposite sides of the earth and thus have generated an elegant solution to the day/night cycle.
The children with Model 8 have finally attained the essence of the
culturally accepted scientific model with a rotating earth, a fixed sun, and
the moon rotating around the earth. It seems likely that even children with
this model have not articuluted their models fully to capture phenomena
such as the time it takes the moon to rotate around the earth or the occurrence of the phases of the moon.
Contrary to our original hypothesis that the stars would also be causally
implicated in the day/night cycle, this belief is not as strong as the belief
that the moon is associated with night. While most of the young children
provided explanations for the disappearance of the stars during the day,
which were similar in kind to the explanations for the disappearance of the
moon, the great majority of the children in our sample thought that the
stars are stationary and knew that it is possible for them to be in the sky during the day but not to be seen because of the brightness of the sun’s light.
Criteria Honored by Children in Constructing Mental Models
We will now examine children’s mental models of the day/night cycle in
terms of the criteria of accuracy, logical consistency, and simplicity.
Accuracy
The mental models of the day/night cycle that the children constructed were
for the most part empirically accurate, in that they were consistent with
children’s observations. One of these observations is that the sun is in the
sky only during the day. The other is the erroneous observation that the
moon is in the sky only during the night. Note that empirical accuracy was
present even in the case of the synthetic models, despite the fact that synthetic models are the products of significant misrepresentations of scientific
information. In fact, it is often the case that the “errors” in the synthetic
models actually increase their empirical accuracy, given the range of observations available to children. For example, the children with models 8 and 9
(Table 9), who assumed that the sun and the moon are fixed on the opposite
sides of a rotating earth, formed models which were empirically accurate
given the (erroneous) observation that the moon is present in the sky only
during the night.
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Logical Consistency
The 38 childrenassignedto a mental model of the earthgavelogically consistent responsesto the four sets of questionswhich investigatedtheir
explanationsof the disappearance
of the sunat night, the disappearance
of
the starsduringthe day, the movementof the moon, andthe alternationof
day and night. In addition, the obtainedmental modelsof the day/night
cyclewereconsistentwith thehypothesizedconstraintsimposedby children’s
mentalmodelsof the earth.Roughlya third of the childrenwho wereput in
the mixed categoriesappearedto be in a transitory state from an initial
model of an up/down moving sunto an earthrotation explanation(Model
13,Table9). Another third appearedto be confusingthe earth’srevolution
aroundthe sunandthe earth’srotation on its axis (Model 14,Table 9). The
final third of the childrenwith mixed modelsgaveresponsesthat werecomplex combinationsof various models.The remaining children’sresponses
wereeitherunspecified(Model 12,Table9) or underdetermined(Model 16,
Table 9).
While our resultsmay appearto contradictreportsthat not only young
children but alsohigh schooland collegestudentsgive internally inconsistent responsesto questionstapping aspectsof their knowledgeof science
(e.g., disessa,1988,1993;Reif & Allen, 1992;Solomon, 1983),this may
not be necessarilythe case.In most of the existingresearchwheresuchinconsistencies
are noted,a studentis consideredto beinternally inconsistent
if he or sheusesa givenscientificconceptcorrectlyin somecasesbut not in
others.The possibility that this studentis using a representationwhich is
different from the scientificone,but which is nevertheless
well-definedand
internally consistentand which can account for the obtained pattern of
“correct” and “erroneous” responses,is usually not exploredin a systematic fashion.Until more detailedanalysisof students’mental representations in theseother domainsis carriedout we will not know if the conflict
betweentheseliteraturesis apparentor real.
Simplicity
In the previoussectionwe arguedthat we were ableto accountfor a large
percentageof our databy assumingthat the childrenin our sampleadopted
well-definedmental models of the day/night cycle which they usedconsistently to answer a number of different questions related to this
phenomenon.In addition to beingsensitiveto issuesto logical consistency,
the childrenalso seemedto showsomesensitivityto issuesof simplicity in
their explanations.
The term simplicity is usedhereto referto the useof the samemechanism
to accountfor different,althoughrelated,phenomenasuchasthe disappearanceof the sunduringthe night andthe apparentdisappearance
of the moon
and starsduringthe day. The findingsof this studyindicatethat the majority
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of the childrenin our sampleusedthe samemechanismto explainthe disappearance of the sunandthe disappearance
of the moon.With the exception
of the children assignedto the occlusionmodel (Model 1, Table 9), there
wasa strongrelationshipbetweenthe specificexplanationgivenfor the disappearance of the sun during the night and of the moon during the day.
Theserelationshipscan be examinedin detail in Table 9. As can be seenin
this table, the children who assertedthat the sun goesdown behind the
mountainsor down to the other sideof the earth alsostatedthat the moon
comesup when the sun goesdown. We call this the “hydraulic model”
becauseit is as if the two movementsare dependenton eachother. The
downwardmovementof the suncausesthe upwardmovementof the moon.
The interdependencyof the movementsof the sun and the moon is
apparentin the other explanationsof the day/night cycle.For example,the
childrenwho said that the sun revolvesaroundthe earth also mentioned
revolutionto be the movementof the moon. We did not find any models
wherethesunrevolvesaroundtheearthbut themoon movesin an up/down
directionor the reverse.Finally, most of the childrenwho adoptedthe explanationin which the day/night cycleis causedby the earth’srotation conceptualizedboth the sunandthe moon asstationary.Again, wedid not find
any instanceswherethe earth wasseenas rotating aroundits axis, the sun
wasstationary,andthe moon movedin an up/down direction,althoughwe
hadthe scientific model wherethe earth rotatesaround its axis, the sun is
stationaryand the moon revolvesaround the earth.
Note that children’smodel of an earthrotating in an up/down direction
with the sun and moon fixed at oppositesidesis a simpler model than the
scientificmodelin which the moon revolvesaroundthe earth.It is the occurrenceof modelssuch as this that lend such strong support to the overall
“constructivist” position.
Explanationsof the disappearance
of the starsat night werenot ascoordinatedwith the disappearance
of the sunand the moon aswasthe caseof
themoonand sunthemselves.With theexceptionof the childrenwho attributedtheday/night cycleto the up/down movementof the sun,of the moon,
andof the starson the othersideof the earth,a differentspecificmechanism
wasusedto explainthe disappearance
of the starsduringthe night than the
oneusedto explainthedisappearance
of thesunandthe moon. In addition,
thegreatmajority of the olderchildrenin our sampleknewthat the starsare
presentduringthe daybut that wecannotseethem becauseof the brightness
Of the sun’s light and gavethis as the explanationfor their apparentdisappearance
during the day.
TOconclude,the findings from the presentstudyshowthat the majority
of the childrenin our sampleformed empiricallyaccurateandlogicallyconsistentmental modelsof the day/night cycle.In addition, their modelsexhibited systematicrelationsbetweenthe mechanismsused to explain the
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disappearance
of the sunandthoseusedto explainthe disappearance
of the
moon which showedconsiderablesensitivityto issuesto simplicity. These
findings agreein generalwith resultsobtainedby Samarapungavan
(1992)
showingthat whenchildrenchoosebetweentheoriestheypreferexplanations
which are empirically accurateand logically consistent.While children
demonstrateconsiderableskills in constructingand modifying their mental
modelsto fit the availabledata,the presentresultsdo not showthat children
have developedmetaconceptualawarenessand consciouscontrol of their
mental models(D. Kuhn, 1989).
The Nature of Conceptual Change
The initial models of the day/night cycle in which the sun moves down
behindthe mountains,goesout into space,or is occludedby oloudsarevery
different from the culturally acceptedmodel of a stationarysun, the earth
rotating around its axis, and the moon revolving around the earth. Our
resultsshow that six-year-oldchildren come to school having formed an
initial model of the day/night cyclewhich, over a period of years,changes
to a syntheticmodel and then to a scientific model. How canwe bestcharacterizethe kind of conceptualchangewhich takes place during the elementary school yearsas the cultural knowledgehas a greaterand greater
impact on the children’smodelsof the day/night cycle?
Accordingto Spelke(Ml), conceptionsof physicalobjectsdo not undergo
fundamentalchangewith development,and knowledgeof the sort we have
calledontologicalpresuppositions
(e.g.,the continuityandsolidityof physical
objects)continuesto beentertainedin adults’commonsense
reasoningabout
physicalobjects.One kind of fundamentalknowledgeabout the behavior
of physicalbodiesrelevantto the issuesdiscussedin this paperis the concept
of an up/down gravity. This is the knowledgethat “unsupportedthingsfall
in a downwarddirection,” which appearsto be presentevenin 6-month-old
infants (Needham& Baillargeon,1993;Spelke,1991).Our resultsshowthat
children’spresuppositionsregardingan up/down gravity needto berevised
and arerevisedby the elementaryschoolchildrenwho providescientific or
even synthetic explanationsof the day/night cycle. We interpret these
resultsto indicatethat the processof knowledgeacquisitioncannotbe fully
accountedfor using the notion of enrichment(Spelke,1991).
In an important recentbook on conceptualchangein scienceThagard
(1992)arguesthat conceptsare organizedin theorieswhich are primarily
structuredvia kind and part-wholehierarchies.Viewed in this way, conceptual changemay involve the addition or deletionof concepts,or their
transformations.The transformationscan be simple-when they involve
differentiation or coalescence;or complex-when they involve alterations
in kind relationsor part relations.Thagardcalls onesuchchange“branch
jumping” sinceit involvesthe movementof a conceptfrom onebranchof
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CYCLE
(A) From Ptolemy to Copernicus
Major Bodies
(B) From Grade 1 to Grade 5
Figure
6. Changes
in the system
of categorization
of the major
astronomical
bodies.
the kind-hierarchy to another. An example of branch jumping which, according to Thagard, is one of the most radical kinds of conceptual change characterizing scientific revolutions, is illustrated in Figure 6. This figure describes
the move from the Ptolemaic system’s classification of the celestial bodies
(Figure 6a) to the modern, Copernican view. Copernicus reconceptualized
the earth as a planet and reclassified the moon as a satellite of the earth.
(The sun was not recognized as a star until around 1800.)
Another important recent approach to conceptual change is found in the
work of Chi and her colleagues (Chi, 1992; Chi, Slotta, & de Leeuw, in
press). Chi has described conceptual change in terms of a special kind of
branch jumping which involves two ontologically distinct categories. According to this theory, conceptual changes take place when a concept belonging
to one ontological category (e.g., matter) is re-assigned to a different ontological category (e.g., process) as was the case historically with the concept
of heat.
The results of the present study support Thagard’s (1992) and Chi et al.‘s
(in press) analysis. Children’s categorization of astronomical objects seems
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to undergoa kind of branchjumping which is similar to the onewhich took
placein the history of science.As shownin Figure6b, six-year-oldchildren
with initial mental modelsof the day/night cyclethink that the earth is a
physicalobject while the sun and the moon are celestialobjects.We have
arguedthat the mental representationof the earth as a spheresurrounded
by spaceis a precondition for understandingthe scientific explanationof
the day/night cycle. In the cosmologyof the third graderwho providesa
scientificexplanationof the day/night cycle,the earthhasbeenreclassified
asa celestialbody, a planet,whichrotatesaroundits axisandrevolvesaround
the sun. At the sametime, the sun, the moon, and the starsare clearlydifferentiated,the child havingrecognizedthat the moon is not causallyrelated
to the day/nightcycle,andthat the starsaredifferent from theothercelestial
bodies.Thus, our datashowthat the developmentof children’scosmologies
provide evidencefor the sametypesof radical conceptualreorganizations
that haveoccurredin the history of science,.
Onelimitation of theThagard(1992)and Chi et al. (in press)approaches,
however,is that they do not explainwhy the reorganizationsof knowledge
which are characterizedas branchjumping are so difficult for scientistsin
the developmentof scienceor for childrenacquiringnewknowledge.Thagard
(1992)acknowledgesthat branchjumping is the product of revolutionary
changesin scientists’underlyingsystemsof beliefs,but doesnot go further
to explainthe natureof thesebeliefsandtheir changes.In our work wehave
adopteda semanticratherthan a syntacticdescriptionof conceptualchange.
We try to characterizethe kinds of knowledgestructuresthat underly children’s mental models of the day/night cycle and to describethe changes
that happenin thesestructuresduring the knowledgeacquisitionprocess.
Fundamentalto our way of thinking is the notion of constraint.We have
argued that the reorganizationsof knowledgetaking place during the
knowledgeacquisitionprocessoccur via the reinterpretationof a hierarchy
of constraintswhich differ in their degreeof entrenchment.The deepestand
most difficult constraintsto changearethoseweterm presuppositions.Presuppositionsform the basisof an individual’s ontology and epistemology
and exert an enormousinfluenceon the knowledgeacquisitionprocess.
In addition to the presuppositions,our theoreticalframeworkincludesa
number of additional constructssuchas beliefs and mental modelswhich
appearto act as second-orderconstraintson the knowledgeacquisition
process,Beliefsand mental models are examplesof what Keil (1990)calls
“acquired-domain-specific”constraints.Thesearethe kinds of constraints
which developwith the acquisitionof expertise,asthestructureof the information learnedcomesto exertits own uniqueinfluenceon the knowledge
acquisition process.Our data suggestthat constraintsof this type come
to exert a powerful role in the child’s understandingof complexphysical
phenomena.
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181
The accountof conceptualchangepresentedin this paperis in someways
similar to the accountof theorychangedevelopedby Carey(1985;1991)but
&O
differs from it in important respects.Careyproposesthat childrenstart
by holding theory A and then switch to theory B which differs from the
originaltheoryin termsof its structure,the phenomenait explains,and the
individual conceptsit includes.In our approachthe theory-like natureof
the structuresunderlyingchildren’sperformanceis tracedto a set of presuppositions,beliefs, and mental modelswhich constrainthe way a given
child will representa specificsituation. Within this theoreticalframework,
conceptualchangeis a continuousprocesswhich happensasthe different
kindsof constraintsmentionedabovearereinterpretedduringthe knowledge
aquisitionprocess.Oneof the advantagesof the presentapproachis that it
canaccountfor thegradualnatureof conceptualchangeandfor the formation of syntheticmodelsof the world.
CONCLUSIONS
Theresearchdescribedin this article attemptedto identify and characterize
elementaryschool children’s mental models of the day/night cycle. The
resultsshowedthat the majority of the studentsin our sample(38out of 60)
useda well-definedmentalmodel of the day/night cycleto answerour questions.Thesemodelswerelogicallyconsistentand for the most part werealso
characterizedby empirical accuracyand simplicity. Initial mental models
showedno influencefrom the currently acceptedscientific explanationof
theday/night cycle,while syntheticmental modelsrepresentedattemptsto
assimilatethe scientific explanationsto existing conceptualstructures.A
theoreticalframework wasoutlined which is capableof explainingthe formationof initial andsyntheticmodelsby postulatingthat thereis a hierarchy
of constraints-presuppositions,
beliefs,andmentalmodels-some of which
arepresentearlyin the child’s life and otherswhich emergelater out of the
structureof the acquiredknowledge,andwhich guidethe knowledgeacquisition process.
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