[forthcoming in The Journal of the History of Ideas]
Galileo’s Interventionist Notion of “Cause”1
Steffen Ducheyne
1. Introduction
In this essay, I shall take up the theme of Galileo’s notion of cause, which has already
received considerable attention.2 I shall argue that the participants in the debate as it stands
have overlooked a striking and essential feature of Galileo’s notion of cause. Galileo not only
reformed natural philosophy, he also – as I shall defend – introduced a new notion of causality
and integrated it in his scientific practice (hence, this new notion also has its methodological
repercussions). Galileo’s conception of causality went hand in hand with his methodology (see
section 3). This is the main message of this essay. It is my claim that Galileo was trying to
construct a new scientifically useful notion of causality. This new notion of causality is an
interventionist notion. According to such a notion, causal relations can be discovered by
actively exploring and manipulating natural processes. In order to know nature we have to
intervene in nature. Generally: If we wish to explore whether A is a cause of B, we will need to
establish whether deliberate and purposive variations in A result in changes in B. If changes in
A produce changes in B, the causal relation is established. It will be shown that this notion first
emerged from Galileo’s work in hydrostatics and came to full fecundity in his treatment of the
tides.
Let me first of all take stock of the present discussion. De Motu is one of Galileo’s early
scientific works on what we today would roughly call ‘mechanics’ (written between 1589 and
1592). That in De Motu Galileo wishes to establish a causal explanation of motion (and
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acceleration) is accepted by all scholars.3 According to Galileo, falling bodies are moved by an
internal cause; projectiles by an external one.4 Galileo indeed claims that he wished to
determine the hidden causes of observable effects “for what we seek are the causes of effects,
and these causes are not given to us by experience)”.5 In dealing with the cause of acceleration,
Galileo clarifies that he wants to discover the true, essential and not the accidental cause of
acceleration.6 Acceleration is an accidental feature of motion, caused by the gradual overtaking
of the intrinsic weight of a body during fall, after being lifted (and the weight being
diminished) by an impressed force. Scholars begin to disagree however on the presence and
importance of causal explanations in the period after this early work. Edwin A. Burtt, echoing
Ernst Mach, wrote that Galileo’s studies on motion led him to focus more on the how than on
the why of motion.7 Closely connected to this is Galileo’s ban of final causes from natural
philosophy.8 Galileo, according to Burtt, treated motions as the secondary causes of natural
phenomena and the forces producing them as their primary causes (of which the nature or
essence is further unknown).9 We only know quantitative effects of forces in terms of motion.10
This implies that knowledge of primary, essential causes is impossible according to Galileo.
After Burtt, authors have gone even further: they questioned the presence of causal explanation
in toto in Galileo’s (mature) work. On the one side of the spectrum, Drake claims that Galileo
banished causal inquiries from his science, since they were speculative and unnecessary:
The word cause, frequent in this early book, is less frequent in the later ones. It
played little part in Galileo’s mature presentation of scientific material, which he
confined more and more to observational and mathematical statements.11
Causal claims were present in his early work (e.g. in the discourse on floating bodies (1612)),
but not in his mature work (by which Drake apparently means the Dialogo and the Discorsi).12
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Pietro Redondi seems to side with Drake: Galileo was defending a docta ignorantia with
respect to causes and causal knowledge.13 There are some passages which seem to converge to
this interpretation (note that they can be made consistent with the causal interpretation as well).
For instance, after having reviewed various hypothetical explanations of the cause of gravity,
Salviati says:
Now, all these fantasies, and others too, ought to be examined; but it is not really
worth while. At present it is the purpose of our Author merely to investigate and
to demonstrate some of the properties of accelerated motion (whatever the cause
of this acceleration may be) (…).14
Ernan V. McMullin, however, correctly argues that this passage in the Discorsi does not
necessarily mean a rejection of causal explanation: It simply means that dynamics needs to be
preceded by kinematics.15 Only when the properties of motion have been described, can we
start with explaining them causally. This does not necessarily entail a rejection of causal
explanation as such.
On the other side, there are authors who stress the importance of causal explanation and
causal reasoning in Galileo’s work and relate them to past traditions where causal knowledge
was important. Peter K. Machamer argued that Galileo’s notion of cause is that of the tradition
of the mixed sciences (“scientiae mixtae”):
I shall attempt to show that though Galileo does use such causal language with
serious intent, there is a sense in which Drake is right about Galileo’s unconcern
for causes; Galileo is, for the most part but not all always, unconcerned about
extrinsic, efficient causes. This is one aspect familiar to those who deal with the
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mixed sciences. Galileo is concerned very much with formal and final causes, and
sometimes material causes.16
He admits that his analysis is primarily based on the Discorsi.17 According to Machamer,
proper (causal) explanations refer to formal, final and material (necessitating) causes.18
William W. Wallace has connected Galileo’s notion of cause to the Aristotelian tradition.19
Galileo frequently uses causal parlance which is in agreement with Aristotle’s views of causes
and his ideas on scientific method laid down in the Posterior Analytics. Galileo’s scientific
demonstrations agree to and are derived from, as John H. Randall first argued, the regressus
strategy in the Aristotelian tradition.20 Wallace’s main message is that Galileo’s nuove scienze
were not created de novo. Jacopo Zabarella was, as Randall claimed, “the methodologist who
stood behind Galileo’s early account of demonstrative methodology”.21 Galileo continued to
use the regressus throughout his career with various modifications.22
Causal explanations are certainly present in Galileo’s work.23 That is presently not the issue
at stake:
The problem of causality in his science is clearly not whether he sought causal
explanations, but rather how he sought them and how he thought they could lead
to certain and unrevisable knowledge about the physical world.24
I would add to that list that in addition to this we also need to clarify what Galileo’s notion of
cause was. In this essay, I shall not directly evaluate Wallace’s and Machamer’s readings. My
point is rather different: instead of solely focussing on past traditions from which much of
Galileo’s terminology appears to be derived, we should pay more attention to some of the
innovative features of Galileo’s notion of causality. There are prima facie parallels with past
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traditions and indeed Galileo frequently used Aristotelian terminology. But, let us not
equivocate Galileo’s notion of ‘cause’ with that of a past tradition too fast. Let us also look at
possibly original contributions of Galileo to the idea of cause. 25 This is the aim of the present
essay: to point to the interventionist strand in Galileo’s conception of cause.
In section 2 I shall therefore begin by carefully looking at some of Galileo’s causal reasoning
strategies. I shall discuss Galileo’s treatment of the floating and sinking of bodies in water and
his explanation of the tides. I have chosen these cases, because on these occasions Galileo is
very explicit on his causal reasoning and his notion of ‘cause’. These cases will pave the way
for a more elaborate understanding of Galileo’s notion of cause. In section 3, I shall compare
Galileo’s interventionist notion of cause with James Woodward’s recent theory of causation,
presently one of the most developed interventionist accounts of causation. In the final section
(4), I shall briefly point to the significance of Galileo’s interventionist notion of cause in
connection to the idea of what Antonio Pérez-Ramos has called an “active science”.26
2. Galileo and the Occurrence of Physical Causes in his Scientific Work
In 2.1.1 and 2.2.1, we shall look at two case-studies in Galileo’s works (one stemming from
the mid-period of his scientific career and one from his later work) where he explicitly
discusses the notion of physical cause. These cases will give us access to Galileo’s notion of
cause. This will set the stage for a fuller discussion of Galileo’s notion of physical cause in
sections 2.1.2 and 2.2.2. The goal of this section (2) is to penetrate the deeper conceptual strata
of Galileo’s notion of ‘cause’. I attempt to characterize Galileo’s notion of “cause” in the form
of three general statements, which are meta-level descriptions of Galileo’s notion of “cause”.
2.1. The Emergence of ‘Cause’ in the Discourse on Floating Bodies (1612)
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2.1.1. Galileo’s Causal intuitions in the Discourse on Floating Bodies
Galileo’s discourse on floating bodies (first edition: 1612) was a best-selling book in its own
time. Unfortunately, it has received relatively little attention by scholars. 27 It is certainly
relevant for an understanding of Galileo’s notion of physical cause, since Galileo explicitly
addresses the problem of finding true causes. Stillman Drake suggests that, when Galileo first
sharply defined the word “cause” for use in scientific inquiries, the “process by which causes
gave way to laws in science may be considered as having begun”.28 In this discourse Galileo
refuted the Aristotelian explanation of floating. The Aristotelians, like Lodovico delle
Colombe, asserted that bodies floated on water because of their flat shape which prevents its
piercing the water’s resistance to division.29 Lodovico delle Colombe claimed to have refuted
Galileo by the following experimentum crucis: a flat ebony chip floats, while an ebony ball of
the same weight cannot do so.30 The central tenet of the Aristotelians was water’s resistance to
division. This tenet was based rather on the metaphysical assumption that all motion requires
an opposing medium, and not on experiments.31 Galileo claimed – in agreement with
Archimedes – that “only greater or lesser heaviness in relation to water” is the cause of floating
or sinking.32 Both parties claimed to have inferred the cause of floating bodies. How do we
know what is the true cause?
Galileo, in defending his position, often argued about what a ‘(proper) cause’ precisely is. In
his notes early in the hydrostatic discussion (and not in the discourse itself), Galileo wrote that
“Causa è quella, la qual posta, sèguita l’effetto; e rimossa, si rimuove l’effetto” (“Cause is that
which put [placed], the effect follows; and removed, the effect is removed.” (sic)).33 This
definition seems to have guided him in his scientific research. Galileo set out to search for the
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“true, intrinsic, and entire cause of the rising and floating of some solid bodies in water”. 34 He
wrote:
With a different method and other means I shall seek to reach the same conclusion
[as Archimedes], reducing the causes of such effects to principles more intrinsic
and immediate, in which are perceived also the causes of some admirable and
almost incredible events, as that a very small quantity of water may raise up and
sustain with its small weight a solid body that is a hundred of thousand times
heavier = the famous hydrostatical paradox. And since demonstrative advance
requires it I shall define some terms and then explain some propositions from
which, as from things true and noted, I may then serve my own purposes.35
The terms Galileo refers to are specific weight, i.e. the weight of a body in a given volume,
absolute weight, i.e. the ‘normal’ weight of a body, and the moment. On “moment” Galileo
writes:
Moment, among mechanics, means that force, that power, that efficacy, with
which the mover moves and the moved resists, which force depends not simply on
weight, but on speed of motion [and] on different inclinations of the spaces over
which motion is made – for a heavy body descending makes greater impetus in a
steeper space than in one less steep. And in short, whatever be the cause of such
force, it always keeps this name of moment.36
The first proposition that follows from these concepts is that if two bodies on a balance have
equal absolute weight, their moment will be equal. Hence, they make equilibrium. 37 The
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second proposition is that the moment and the power of heaviness is increased by the speed of
motion.38 Then Galileo started laying down further physico-mathematical theorems and
experiments, which confirmed that the sinking or floating of bodies is dependent on their
specific heaviness.39 These propositions indeed “opened the road to the contemplation of the
true, intrinsic, and proper cause of the diverse motions and of rest of different solid bodies in
various mediums”.40 Galileo claimed that bodies sink or float irrespective of their form. 41 This
can be shown by experiments where the (specific) weight is kept fixed and the form is varied:
Therefore, commencing to investigate with examination by exact experiment how
true it is that shape does not at all affect the sinking or not sinking of the same
solids, and having already demonstrated how a greater heaviness of the solid with
respect to the heaviness of the medium is the cause of its ascending or
descending, [then] whenever we want to make a test of what effect diversity of
shape has on the latter, it will be necessary to make the experiment with materials
in which variety of heaviness does not exist. For were we to make use of materials
that could vary in specific weight from one to another, when we encountered
variation in the fact of descent or ascent we would always remain with ambiguous
reasoning as to whether the difference derived truly from shape alone, or also
from different heaviness.42
Form is a cause secundum quid, it functions as an assisting or concomitant cause.43 It can
influence the speed of descent or ascent, but it is not as such the cause of its upward and
downward motion. It is a secondary cause, not a primary cause.44 The prima facie anomalous
floating of the chip is then explained as follows. The chip, upon closer inspection, is immersed
under the water level with a layer of air above it. This layer and the original chip form an
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aggregate which is specifically lighter than water. Hence its will (nearly) float. The form of the
chip is not the true cause of its floating. The form does allow for the air to take its space above
the chip, but it is the presence of the air that produces the lighter-than-water-aggregate. This
lighter-than-water-aggregate is the true cause. Scientific understanding for Galileo was
discovering the proximate and immediate causes of phenomena. True causes are the immediate
causes not the mediate ones.45
2.1.2. A More Systematic Analysis of Galileo’s Causal Intuitions in the Discourse on
Floating Bodies
Let us take stock and characterize Galileo’s notion of cause in the discourse on floating
bodies. We have seen that Galileo conceived of a true cause as the most proximate and
immediate factor that brings an effect about. Without that factor the effect would not occur.
Whether an effect is directly produced by a property can be established by varying this
property, while keeping all other properties fixed. If the effect follows, the property under
investigation is the true cause. If the effect does not follow, the property is not the true cause. A
true cause needed to refer to some essential property of the object under investigation (of
course, distinguishing between essential properties and accidental ones is sometimes a
precarious work).46 In the discourse form is an accidental property, while specific weight is
not. Based on this, we can see that one of the Galileo’s early strategies for causal reasoning is
isolating and varying the presumed causal factor (IVC):
(IVC):
If, when keeping fixed all other relevant causal factors (Px), varying property P1 (= the
assumed causal factor) results in an alteration of property E1 (= the effect), then we may
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conclude that P1 is a causal factor for E1 (or as Galileo would formulate it “a true
cause”).
In Bodies That Stay Atop Water or Move in It, Galileo typically assumes that a true cause is
universal in the sense that is responsible for all observable floating or sinking behaviour. This
is, what I would call, the universality and uniqueness assumption (U²) of Galileo’s notion of
‘cause’:
(U²general):
If P1 is a true cause of E1, then P1 is a universal and unique cause, i.e. it explains
all E’s similar to E1 (under all circumstances).
(U²sinking or floating):
If P1 (specific weight) is a true cause of E1 (the sinking of lead or the floating of
olive oil) then P1 is a universal and unique cause, i.e. it explains all E’s similar to
E1 (the floating or sinking behaviour of all bodies under all circumstances).
In other words, two generalisations are made: (1) the causal relation as such and (2) the fact
that the inferred cause is assumed to be a unique cause, i.e. that it explains all similar
phenomena (or put differently, that similar phenomena cannot be caused by different causes).
Post factum, we might of course say that Galileo’s universality assumption was incorrect, since
it is not unimaginable to find similar effects which are produced by different causes. It is not
possible to explain all phenomena of sinking and floating solely by specific weight. According
to the modern explanation, the direct cause of the floating anomalous chip is the surface
tension of the water. This is a case where one causal factor (surface tension) nullifies another
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causal factor (greater specific heaviness with respect to water). According to Galileo’s
reasoning the lighter-than-water-aggregate of ebony and air is the direct cause of the floating of
the chip. This explanation is introduced ad hoc, after Galileo’s statement that specific
heaviness with respect to water is the true cause. Galileo’s true cause turned out not to be
unique.
2.2. The Causal Explanation of the Tides in the Dialogo (1632)
2.2.1. The Causal Intuitions in the Explanation of the Tides
Although Galileo’s theory of the tides has received relatively few attention 47, the theory was
to Galileo’s mind the “principal event” in the Dialogo.48 In the Fourth Day of the Dialogo
(1632), Galileo presents his geo-kinetic theory of the tides. An early version of this theory was
written in 1616: Discorso del flusso e reflusso del mare.49 I shall focus on the later version
from the Dialogo. The tides were to Galileo’s mind a physical proof that the earth moved.50
Salviati (Galileo’s spokesman) stresses that in dealing with questions like these “a knowledge
of the effects is what leads to an investigation and discovery of the causes”. 51 Such an
investigation may lead to the “true and primary”52, or “universal causes”53 of the effects we
observe. Galileo acknowledges that not “all proper and sufficient causes” will be adduced. In
renouncing other alleged explanations, which Galileo calls “occult qualities” or “idle
imaginations”54 (e.g. various depths of the sea, attraction or heat produced by the Moon),
Salviati formulates a positive criterion for a true cause (“vera causa”), namely artificial
reproduction:
10
But I believe that you have not any stronger indication that the true cause of the
tides is one of those incomprehensibles than the mere fact that among all things so
far adduced as verae causae there is not one which we can duplicate for ourselves
by means of appropriate artificial device. For neither by the light of the moon or
sun, nor by temperate heat, nor by differences of depth can we ever make water
contained in a motionless vessel run to and fro, or rise and fall in but a single
place. But if, by simply setting the vessel in motion, I can represent for you
without any artifice at all precisely those changes which are perceived in the
waters of the sea, why should you reject this cause and take refuge in miracles?55
Galileo even claimed to have “a mechanical model” of the tides.56 Unfortunately, he did not
further discuss it.57 Galileo then presented his kinematical model of the tides.58 He explicitly
renounced an explanation involving attractions of the Moon like the one favoured by Kepler. 59
The uniform annual motion60 of the Earth from west to east (depicted by circle BC) and the
uniform diurnal motion of the Earth from west to east (depicted by circle DEFG), result in an
uneven mixed motion in the different parts on the earth (see figure 1).
Figure 1. The earth’s annual and diurnal motion.
At point D the absolute motion will be the swiftest, since both motions act in the same
direction. At point F the contrary will occur. At points E and G the absolute motion remains
equal to the simple annual motion. The cause of the tides is the acceleration and deceleration of
different parts of the earth which results from its diurnal and annual rotation. Paolo Palmieri
uses the expression “tide-generating acceleration”.61 Indeed, when we accelerate and decelerate
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a vessel with water contained in it, we observe that the water will run back and forth. 62 Galileo
notes that:
Now this is the most fundamental and effective cause of the tides, without which
they would not take place. But the particular events observed at different times
and places are many and varied; these must depend upon diverse concomitant
causes, though all must have some connection63 with the fundamental cause. So
our next business is to bring up and examine the different phenomena which may
be the causes of such diverse effects.64
Next, Galileo discusses the concomitant or particular causes. The first of these concomitant
causes is the tendency of water “by its own weight” to return to equilibrium and pass beyond it
and to continue to do so until its impetus has diminished. The second is the length of the
vessel: in shorter vessels the oscillations will be more frequent; in longer ones less frequent.
The third is the depth of the vessel: in deep vessels oscillations will be more frequent than in
less deeper ones. The fourth is that the oscillations produce two motions: a rising and falling at
either extremity (= vertical displacement) and the horizontal running to and fro (= horizontal
current). The fifth is the inequality of the acceleration and deceleration communicated to
different parts at great distance from each other at the same moment. The effects of the fifth
concomitant cause are so fine-grained that “it is impossible for us to duplicate its effects by any
practical experiment”.65 These secondary causes are adduced to explain the six-hour periods in
the Mediterranean (the primary cause would by itself give rise to a twelve-hour period).
Galileo states that:
12
These causes, although they do not operate to move the waters (that action being
from the primary cause alone, without which there would be no tides), are
nevertheless the principal factors in limiting the duration of the reciprocations,
and operate so powerfully that the primary cause must bow to them.66
Galileo strengthens his claim by pointing out that “from one uniform cause only one single
uniform effect can follow” and that “effects, being contrary and irregular, you can never
deduce from one uniform and constant cause”.67 Galileo used a principle of superposition to
explain the interaction of the tide-generating acceleration and the oscillatory properties of the
seabed. He did not have the mathematical tools to deal with this problem. According to Galileo
“there is only one true and primary cause for one effect”. 68 That Galileo’s kinematical model is
highly connected with his ideas on physical causes, can be seen from the following fragment:
Thus I say if it is true that one effect can have only one basic cause, and if
between the cause and the effect there is a fixed and constant connection, then
whenever a fixed and constant alteration is seen in the effect, there must be a
fixed and constant variation in the cause. Now since the alterations which take
place in the tides at different times of the year and of the month have their fixed
and constant periods, it must be that regular changes occur simultaneously in the
primary cause of the tides. Next, the alterations in the tides at the said times
consist of nothing more than changes in their size; that is in the rising and
lowering of the water a greater or lesser amount, and its running with greater or
lesser impetus. Hence it is necessary that whatever the primary cause of the tides
is, it should increase or diminish its force at the specific times mentioned.69
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Again we encounter Galileo’s universality assumption. Let us use this presentation of Galileo’s
theory of the tides as starting point for an analysis of Galileo’s notion of physical cause.
2.2.2. A More Systematic Treatment of These Intuitions
Being able to reproduce the observed effect by means of a mechanical model is one of
Galileo’s criteria for establishing causal relations between events. In the case of the tides it is
impossible to manipulate or control the kinematical properties of the earth. Therefore, Galileo
uses what he thinks is a representative small-scale model which reproduces and isolates the
kinematical properties of the earth. This model is similar qua kinematical properties to the
earth. The model obviously does not take into account the form of the seabed. The motions of
the model indeed result in to and fro motion. Hence, Galileo concludes that the tides are caused
by a similar acceleration. I refer to this strategy as artificial reproduction (AR):
(AR):
If a representative physical model M, similar qua property P to a physical system
φ, produces in virtue of P certain regular effects EM, then P is the primary cause
of the similar and regular Eφ’s.
Galileo uses a replica or simulacrum, which easily allows manipulative operations, to model a
physical system which is physically impossible to manipulate directly. In cases where human
interventions are impossible, Galileo instead manipulates a representative replica in order to
answer his scientific questions. William R. Shea correctly noted:
14
It is one of Galileo’s great contributions to the development of the scientific
method that he clearly recognised the necessity of isolating the true cause by
creating artificial conditions where one element is varied at a time.70
Bear in mind that it was Galileo’s main point to show that the tides are produced by a mixed
motion. Galileo’s strategy is strongly based on his principle that “there is only one true and
primary cause for one effect”. Since Galileo accepts this principle as a true maxim he may
easily infer that the cause of the effects of the model is identical to the cause of the effects of
the physical system. Since they are the same effects, they are produced by the same cause (cf.
Galileo’s U assumption). Despite Galileo’s insistence on finding universal causes, he had to
take into account secondary causes to explain the tides. The observed effects are highly
irregular. To explain these irregularities Galileo ad hoc adduces the secondary causes: the
tendency of water to equilibrate itself, the depth of the sea, the breadth, … etc. These
secondary causes disturb the regular effects.
3. Contempory Interventionist Intuitions
In this section, I shall briefly compare Galileo’s intuitions on causation with one of the
central contemporary interventionist accounts on causation in the philosophy of science.
Contemporary philosophers of science have attempted to develop and elaborate an
interventionist or manipulationist account of causation and explanation.71 I shall focus on
James Woodward’s account. His account is meant as a theory of causal explanation. Such an
account holds that causal and explanatory relations are “relationships that are potentially
exploitable for purposes of manipulation and control” and that these relationships are
“invariant under interventions”.72 It is my claim that Galileo had similar interventionist or
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manipulationist intuitions on causation. Let us first look at Woodward’s modern interventionist
intuitions.73 It is not my aim here to present a complete survey of Woodward’s theory of
causation, nor to evaluate Woodward’s proposal, but only to touch upon those matters that are
relevant to a fruitful comparison with Galileo. To Woodward’s mind causes are “potential
handles or devices for bringing about effects”.74 Judea Pearl labels causal networks as “oracles
of intervention”.75 Of crucial importance are Woodward’s notions of intervention variable and
invariance. If X and Y are two variables with different values, I is an intervention variable for
X with respect to Y, if and only if, the following criteria hold:
(IV)
I1. I causes X.
I2. I acts as a switch for all other variables that cause X. That is, certain values of I are
such that when I attains those values, X ceases to depend on the values of other variables
that cause X and instead depends only on the value taken by I.
I.3. Any directed path from I to Y goes through X. That is, I does not directly cause Y and
is not a cause of any causes of Y that are distinct from X except, of course, for those
causes of Y, if any, that are built into the I-X-Y connection itself; that is except for (a) any
causes of Y that are effects of X (i.e., variables that are causally between X and Y) and (b)
any causes of Y that are between I and Y and have no effect on Y independently of X.
I.4 I is (statistically) independent of any variable Z that causes Y and that is on a directed
path that does not go through X.76
Some explanation is in order here.77 The intuitive idea is that I is an intervention variable for X
with respect to Y, when all changes that occur in the value Y are produced only by changes in
the value of X (which are directly brought about by I). I.1 states that the changes in X are
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produced by the intervention I. I.2 tells us that for some values of I, the value of X depends
only on the value of I. In this way, we are able to rule out all other causes of X. I.3 informs us
that I cannot directly cause Y and that I cannot be the cause of another variable (Z) that causes
Y. Finally, I.4 says that there are no other variables, other than I, which produce Y. Woodward
further distinguishes between direct causes and contributing causes: (1) X is a direct cause of
X with respect to some variable set V, if there is a possible intervention of X that will change
Y when all other variables in V besides X and Y are held fixed 78; (2) X is a contributing cause
of Y, if there is a directed path from X to Y such that each link in this path is a causal
relationship.79 The relations we encounter in manipulating nature need to be stable. 80 The
second important notion, besides intervention, for Woodward’s account is invariance. Very
crudely, this notion refers to the fact that the changes produced in Y through X continue to
hold under a certain range of interventions. An invariant relation remains stable as other
changes occur. Typically, we will generalize the result produced by our intervention.
Invariance has to do with the fact that “the generalization should continue to hold under an
intervention that changes its independent variables sufficiently (or in such a way) that the value
of its dependent variable is predicted by the generalization to change under the intervention”.81
Obviously, it is not my claim that Galileo endorsed exactly the same ideas on causation as
Woodward. Galileo’s notion of causation clearly did not incorporate such notions as
“(in)dependent variable”, “statistical probability”, or “invariance under manipulation”. And
that is only for starters. I shall not go into detail and discuss all the differences here, since my
claim focuses on the similarities. What is important is the following. Galileo endorsed the same
intuition on which Woodward’s programme is based: that in order to establish causal relations
we need, while keeping all other possible factors fixed, to manipulate and vary the presumed
cause, whose manipulation and variation will result, if it is a real cause, in a variation of the
effect (a variation in the cause will result in a variation of the effect). In order to control the
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effect, we should manipulate its cause. This interventionist stratum of causation in Galileo’s
natural philosophy has not received much scholarly interest. This intuition, which is explicitly
developed by Woodward (see his definition of direct cause), is embedded in Galileo’s
scientific practice (see section 3.2). It played a highly significant role in Galileo’s practice of
science. This should be clear by now from the discussion in section 3.2. It is one of Galileo’s
strategies for inferring causal relations (IVC). In The Assayer (1623) Galileo explicitly
discusses discovering causal links by intervention:
To discover the true cause I reason as follows: “If we do not achieve an effect
which others achieved, then it must be that in our operations we lack something
that produces their success [“nostro operare manchiamo di quello che fu causa
della riuscita d'esso effetto”]. And if there is just one single thing we lack, then
that alone can be the true cause. (…)”82
Woodward’s idea of direct83/contributing cause roughly corresponds to Galileo’s idea of
proximate/remote cause.
A further important difference between Galileo and Woodward is that Galileo does not only
have an interventionist concept of causation, but that he also has a direct interventionist
methodology. Let me clarify what I mean by that. In his insistence on using a scale-model of
the kinetic properties of the earth, Galileo seems to suggest that proper scientific knowledge
presupposes actually realizable interventions. By contrast, Woodward allows that we may
meaningfully make use of counterfactual claims about what would happen under interventions,
even when such interventions are not physically possible.84 Hence, it makes sense to claim
doubling the moon’s orbit would cause changes in the motion of the tides. Although we cannot
change the moon’s orbit, Newton’s theory shows what would happen to the tides under an
18
intervention that doubles the moon’s orbit, and “this is enough for counterfactual claims about
what would happen under such interventions to be legitimate and to allow us to assess their
truth”.85
4. In Conclusion: Galileo as an “Operative Scientist”
In the seventeenth century scientific practice was increasingly portrayed as a practice
wherein we manipulate and reproduce natural phenomena. In the literature on the emergence of
the idea of science as an operative science (“scientia operativa”), Francis Bacon is usually
given credit for this transformation.86 A knower, according to Bacon, is essentially a maker.
True knowledge refers to knowledge which is made or can be made (reproduced, modelled,
fabricated, …).87 In order to know a phenomenon we should be able to (re)produce it.88 Put
more precisely: “The capacity of (re)producing Nature’s ‘effects’ was perceived as the
epistemological guarantee of man’s knowledge of natural processes in the external world.”89.
Accordingly, Bacon reacted to the Aristotelian dichotomy between products of nature
(“naturalia”) and human arts (“artificialia”), by showing that there is no ontological difference
between the spontaneous workings of nature and the workings which are directed or
manipulated by man’s purposive action.90 Nature always maintains the same modus operandi.
In his third Letter on the Sunspots (1613) Galileo subscribed to this idea:
Nature, deaf to our entreaties, will not alter or change the course of her effects;
and those things that we are here trying to investigate have not just occurred once
and then vanished, but have always proceeded and will always proceed in the
same style.91
19
Hence, there is no fundamental difference between what nature produces herself and what is
brought about by men.
I have argued that there is a significant interventionist component in Galileo’s causal
reasoning and practice. This component played an essential role in Galileo’s scientific practice
and his articulation of the notion of ‘cause’, as can be seen from the examples discussed above.
Galileo subscribed to the idea that if we wish to really understand nature we have to
manipulate and reproduce her. “Nostro operare” is what provides us with a causal
understanding of the world. Galileo was indeed a highly self-conscious operative scientist.
Ghent University, Belgium
20
1
The author is Research Assistant of the Research Foundation - Flanders (FWO - Vlaanderen).
I am indebted to Erik Weber and the anonymous referee for making some interesting points
that allowed me to improve this essay.
2
For two of the earliest scholarly appraisals, see Edwin A. Burtt, The Metaphysical
Foundations of Modern Physical Science, A History and Critical Essay (London: Routledge &
Paul Kegan, [1924] 1967) and Ernst Mach, The Science of Mechanics, A Critical and
Historical Account of Its Development (Illinois: La Salle, [1883] 1974). For the more recent
literature see infra.
See for instance William R. Shea, Galileo’s Intellectual Revolution, Middle Period 1610-
3
1632 (New York: Neale Watson Academic Publications, 1972), 36.
4
Galileo Galilei, On Motion and On Mechanics, Translated with Introduction and Notes by
I.E. Drabkin and S. Drake (Madison: The University of Wisconsin Press, 1960), 6.
5
Ibid., 27.
6
Ibid., 87.
7
See Burtt, The Metaphysical Foundations, 80-81 and Mach, The Science of Mechanics, 155.
Burtt’s analysis is simply refuted by pointing to Galileo’s horror vacui explanation of
8
cohesion. Bodies cohere in order to prevent a vacuum to occur in nature. Galileo Galilei,
Dialogues Concerning Two New Sciences, Translated by Henry Crew and Alfonso de Salvio
(New York: Dover, [1638] 1954), 11-26. For a discussion of Galileo’s argument containing the
rota Aristotelis, see H. E. Le Grand, “Galileo’s Matter Theory,” in New Perspectives on
Galileo, eds. R. E. Butts and J. C. Pitt (Dordrecht/Boston: Reidel, 1978), 197-208.
9
Ibid., 91.
10
Ibid., 93.
21
11
Stillman Drake, Cause, Experiment and Science, A Galilean dialogue incorporating a new
English translation of Galileo’s “Bodies That Stay atop Water, or Move in It”
(Chicago/London: The University of Chicago Press, 1981), xxviii.
12
Drake noted that Galileo’s usage of the word “cause” after 1600 had a “man-in-the-street
ring”, rather than a technical Aristotelian connotation. See Stillman Drake, Galileo at Work,
His Scientific Biography (Chicago/London: The University of Chicago Press, 1978), 33.
13
Pietro Redondi, “From Galileo to Augustine,” in: The Cambridge Companion to Galileo, ed.
P. K. Machamer (Cambridge: Cambridge University Press, 1998), 175-210, 185.
14
Galilei, Dialogues, 166-67; For the original quote see Galileo Galilei, Le Opere di Galileo
Galilei, Nuova Ristampa della Edizione Nazionale (20 vol.), edited by Antonio Favaro
[Giuseppe Saragat] (Florence: Barbèra, 1968), VIII, 202.
15
Ernan V. McMullin, “The Conception of Science in Galileo’s Work”, in New Perspectives
on Galileo, ed. R. E. Butts and J. C. Pitt (Dordrecht/Boston: Reidel, 1978), 209-258, 238.
16
Peter K. Machamer, “Galileo and the Causes”, in New Perspectives on Galileo, ed. R. E.
Butts and J. C. Pitt (Dordrecht/Boston: Reidel, 1978), 161-180, 162.
17
Ibid., 161.
18
Machamer, Galileo and the Causes, 173.
19
See William A. Wallace, Galileo's Early Notebooks: The Physical Questions, A Translation
from the Latin, with Historical and Paleographical commentary (Notre Dame: University of
Notre Dame Press, 1977); William A. Wallace. Galileo and his Sources: the Heritage of the
Collegio Romano in Galileo’s Science (Princeton: Princeton University Press, 1984); William
A. Wallace, “Randall Redivivus Galileo and the Paduan Aristotelians,” Journal of the History
of Ideas 49 (1988), 133-149; William A. Wallace, Galileo’s Logical Treatises, A Translation,
with Notes and Commentary of His Appropriated Latin Questions on Aristotle’s Posterior
22
Analytics, (Dordrecht/Boston/London: Kluwer, 1992); and, William A. Wallace, Galileo, the
Jesuits, and the Medieval Aristotle (Aldershot: Ashgate, 1999).
20
See John H. Randall, “The Development of Scientific Method in the School of Padua,”
Journal of the History of Ideas 1 (1940), 177-206; and Wallace, Galileo’s Logical Treatises,
166-167. The Paduan Aristotelians – exemplified by Jacopo Zabarella – are usually credited
with elaborating Aristotle’s logic of demonstration into a scientific method of demonstration in
which one first reasons from the effects to the causes (resolution), and then from the causes to
the effects (composition). Demonstrative regressus is a procedure which combines an inference
from an observed effect to its proximate cause with an inference from the proximate cause to
the observed effect. See Nicolas Jardine, “Epistemology of the Sciences,” in The Cambridge
History of Renaissance Philosophy, ed. Charles B. Schmitt (Cambridge: Cambridge University
Press, 1988), 685-711. As Peter Dear notes: “By no means wholly original with Zabarella but
closely associated with his name throughout Europe in the later sixteenth and seventeenth
centuries, the technique had developed from a commentary tradition that focused on Aristotle’s
Posterior Analytics, and in particular on Aristotle’s distinction between two forms of
demonstration: apodeixis tou dioti and apodeixis tou hoti, usually latinized as demonstration
propter quid and demonstratio quia.” (Peter Dear, Discipline and Experience, The
Mathematical Way in the Scientific Revolution (Chicago/London: University of Chicago Press,
1995), 27). Randall was unaware of Galileo’s Logical Treatises (BNF MS Gal. 27) (see
Wallace, Randall Redivivus, 133).
21
Wallace, Randall Redivivus, 145.
22
Ibid.
23
See Wallace, Galileo’s Logical Treatises, for several examples ranging from different
periods in Galileo’s career.
24
Wallace, Galileo, the Jesuits, and the Medieval Aristotle, 624.
23
25
I admit that Wallace points to some innovative changes Galileo made to the regressus
methodology. The first is the use of experimental models (Wallace, Galileo, the Jesuits, and
the Medieval Aristotle, 627). The second concentrates on the “various quantitative modalities
of cause-and-effect phenomena” and the use of these “to reason mathematically to the
existence of a physical cause for an observed physical effect” (Ibid., 629). A.C. Crombie has
also hinted to the importance of Galileo of varying the conditions and isolating the causes. See
A. C. Crombie, The History of Science, From Augustine to Galileo (2 vol.) (New York: Dover,
[1952] 1995), II, 147.
26
Antonio Pérez-Ramos, Francis Bacon's Idea of Science and the Maker's Knowledge
Tradition (Oxford: Clarendon Press, 1988); and Antonio Pérez-Ramos, “Bacon’s Forms and
the Maker’s Knowledge,” in The Cambridge Companion to Bacon, ed. M. Peltonen, Markuu
(Cambridge: Cambridge University Press, 1996), 99-120.
27
However, see Paolo Palmieri, “The Cognitive Devolopment of Galileo’s Theory of
Buoyancy,” Archives for the History of the Exact Sciences 50 (2005), 189-222.
28
Drake, Cause, Experiment and Science, xxv.
29
Ibid., xvii.
30
Ibid., xix. Today we would explain this phenomenon by the surface tension of the water.
This was only discovered in the eighteenth century.
31
Ibid., xxiii.
32
Ibid., 23.
33
Ibid., 217. Drake draws an analogy with the expression “causam tollere” that Galileo
probably learned as a medical student (Ibid., xxvii).
34
Ibid., 25.
35
Ibid., 26; Opere, IV, 67.
36
Ibid., 29; Opere, IV, 68.
24
37
Ibid.
38
Ibid., 31.
39
Ibid., 35-49.
40
Ibid., 59.
41
Ibid., 23.
42
Ibid., 74 (emphasis added); Opere, IV, 89.
43
Ibid., 164.
44
In BNF MS 27 (referred to as the Logical Questions) which was written between 1588 and
1591, Galileo introduced various classifications of different causes, among which are the
following: verae causae versus virtual ones, universal versus particular ones, internal versus
external ones, proximate versus immediate ones, … (Wallace, Galileo, the Jesuits, and the
Medieval Aristotle, 611-613).
45
Ibid., 70.
46
This topic is far too complex to spell out here. For the different ways Galileo considered
properties as accidental, see Noretta Koertge, “Galileo and the Problem of Accidents,” Journal
of the History of Ideas 38 (1977), 389-408.
47
Paolo Palmieri, “Re-examining Galileo’s Theory of the Tides,” Archives for the History of
the Exact Sciences 53 (1998), 223-375.
48
Galileo Galilei, S.J. Gould ed., Dialogue Concerning the Two Chief World Systems,
Translated and with revised notes by Stillman Drake, (New York: The Modern Library, [1632]
2001), 479. The most complete and up-to-date treatment is Palmieri, Re-examining. I owe a lot
to Palmieri’s insightful analysis.
49
See Opere, V, 377-395.
50
William R. Shea, “Galileo’s Copernicanism,” in The Cambridge Companion to Galileo, ed.
P. K. Machamer (Cambridge: Cambridge University Press, 1998), 211-243, 224-226. It should
25
be kept in mind, however, that Galileo’s explanation of the tides is one of his “earliest original
physical ideas” (Wallace Hooper, “Seventeenth-Century Theories of the Tides as a Gauge of
Scientific Change,” in The Reception of the Galilean Science of Motion in Seventeenth-Century
Europe, eds. C. R. Palmerino and J.M.M.H Thijssen (Dordrecht/Boston/London: Kluwer,
2004), 199-242, 206). Galileo was aware that the tides were a relevant problem to Copernicus’s
theory by 1595.
51
Galilei, Diaologue, 484.
52
Ibid., 485.
53
Ibid., 533.
54
Ibid., 516.
55
Ibid., 489 (emphasis added); Opere, VII, 447.
56
Galilei, Dialogue, 500.
57
There seems to be historical evidence that Galileo built several mechanical models of the
tides; the details on these devices are lacking (Palmieri, Re-examining, 318-325).
58
Ibid., 495-496.
59
Ibid., 536.
60
In contrast to Aiton, Clavelin, Mach and Shea, Palmieri argues that there is no contradiction
between the principle of relativity formulated in the Second Day of the Dialogo and Galileo’s
theory of the tides (Palmieri, Re-examining, 236-243). The principle of relativity which states
that there is no observable difference of motion applies to uniform motions or motions at rest;
in this case the Earth is a vessel that has a continuous but non-uniform motion (since it is
accelerated and retarded). Differences in motion in this last case can be noticed.
61
Ibid., 232.
62
Galilei, Dialogue, 496-497, 499-500.
26
63
This supposes what we call today a “principle of superimposition” of waves which explains
the interaction of the tide-generating acceleration and the internal properties of the vessel
(Palmieri, Re-examining, 263).
64
Ibid., 497; Opere, VII, 454.
65
Galilei, Dialogue, 498.
66
Ibid., 502; Opere, VII, 458.
67
Galilei, Dialogue, 515.
68
Ibid., 488.
69
Ibid., 517 (emphasis added); Opere, VII, 471.
70
Shea, Galileo’s Intellectual Revolution, 40.
71
For the relevant literature see James Woodward, Making Things Happen, A Theory of
Causal Explanation (Oxford: Oxford University Press, 2003).
72
Ibid., v.
73
Woodward refers to the twentieth-century pioneering work in the area of manipulability
theories of causation of R. G. Collingwood, Douglas Gasking and Georg Henrik von Wright
(Ibid., 12). He correctly states the importance of manipulating or controlling nature in the
development of the history of science. Neglect of this, according to Woodward, originates from
the sharp dichotomy between (pure) science and technology (Ibid., 11).
74
75
Ibid., 12.
Judea Pearl, Causality, Models, Reasoning, and Inference, (Cambridge: Cambridge
University Press, 2000), 22.
76
Woodward, Making Things Happen, 98.
77
Ibid., 99-102.
78
Ibid., 55.
79
Ibid., 57.
27
80
Pearl also stresses the stability inherent in causal relationships. According to Pearl causal
relations are stable, ontological relations, describing objective physical constraints in our world
(Pearl, Causality, Models, Reasoning, and Inference, 25).
81
Woodward, Making Things Happen, 250.
82
Stillman Drake, Discoveries and Opinions of Galileo (New York: Doubleday & Company,
1957, 272 (emphasis added); Opere, VI, 340.
83
Woodward defines a direct cause as follows: X is a direct cause of Y with respect to some
variable set V, if and only if, there is a possible intervention on X that will change Y when all
other variables in V besides X and Y are held fixed at some value by interventions (Woodward,
Making Things Happen, 55). “Possible” does not refer to “realizable by humans”, it refers to
all possible interventions that are logically possible or well-defined (Ibid., 128).
84
Woodward, Making Things Happen, 132.
85
Ibid., 131.
86
See Pérez-Ramos, Francis Bacon's Idea of Science; Pérez-Ramos, Bacon’s Forms and the
Maker’s Knowledge. The tradition of the maker’s knowledge is referred to by Pérez-Ramos as
“one of those ‘subterranean’ currents in Western thought which are only made explicit from
time to time” (Pérez-Ramos, Francis Bacon's Idea of Science, 150). In her innovating work,
Pamela H. Smith also nuances the credit which is usually given to Bacon from a totally
different perspective: “The idea of an “active science,” however, goes back not to Bacon, but
to the writings and of work of art of Dürer, Leonardo, Pailissy, to the makers of the works of
art that filled art and curiosity cabinets, and to the writings and persona of Paracelsus. These
artisans and practitioners appealed to nature as the basis of their science.” (Pamela H Smith,
The Body of the Artisan, Art and Experience in the Scientific Revolution (Chicago: The
University of Chicago Press, 2004), 239). William Eamon further stresses the importance of
the books of secrets (“libri secretorum”), which exhibit a strong utilitarian tendency, in the
28
constitution of a “maker’s knowledge” (William Eamon, Science and the Secrets of Nature,
Books of Secrets in Medieval and Early Modern Culture (Princeton/New Jersey: Princeton
University Press, 1996), 10). These books were based upon a ““down-to-earth”, experimental
outlook: they did not affirm underlying principles but taught “how to”” (Ibid., 4, cf. 126-134).
87
Pérez-Ramos, Bacon’s Forms and the Maker’s Knowledge, 110.
88
Ibid., 115.
89
Pérez-Ramos, Francis Bacon's Idea of Science, 59.
90
Ibid., 109; see also Pérez-Ramos, Bacon’s Forms and the Maker’s Knowledge, 110-116.
William R. Newman, however, tempers Pérez-Ramos’s view by showing that Aristotle already
referred to manufactured analogues of rainbows and that Themo Judaei (fourteenth century)
already testified of a maker’s conception of knowledge (William Newman, Promethean
Ambitions, Alchemy and the Quest to Perfect Nature (Chicago/London: The University of
Chicago Press, 2004), 242, 247-248.
91
Drake, Discoveries and Opinions of Galileo, 136; Opere, V, 218-219.
29