On What Goes On:
The Ontology of Processes and
Events
Antony Galton
University of Exeter, UK
How are processes related to
events?
• Mourelatos (1981): Process and Event are
disjoint subcategories of Occurrence.
• Moens and Steedman (1988): Process is a
subcategory of Event.
• Sowa (2000): Event is a subcategory of
Process.
• Worboys (2004): ‘One person’s process is
another’s event, and vice versa’.
Dictionary definitions
(C.O.D., 5th edition, 1964)
• Event. Fact of a thing’s happening; thing that
happens, esp. important thing; any of several
possible but mutually exclusive occurrences;
something on the issue of which money is
staked; result; outcome.
• Process. Progress, course; course of action,
proceeding, esp. method of operation in
manufacture, printing, photography, etc.; natural
or involuntary operation, series of changes
• These definitions have virtually nothing in
common!
Dictionary definitions
(C.O.D., 8th edition, 1990)
• Event. A thing that happens or takes place, esp.
one of importance; the fact of a thing’s occurring;
a result or outcome; an item in a sports
programme, or the programme as a whole.
(Physics) a single occurrence of a process, e.g.,
the ionisation of one atom; something on the
result of which money is staked.
• Process. A course of action or proceeding, esp.
a series of stages in manufacture or some other
operation; the progress or course of something;
a natural or involuntary operation or series of
changes; an action at law, a summons or writ.
A Simple Ontology
Continuants
• Continuants endure through time; hence,
they are also called endurants.
• A continuant exists as a whole at each
moment of its existence.
• A continuant can undergo change: i.e., its
properties may be different at different
times, although its identity remains fixed.
• It may have spatial, but not temporal parts.
Occurrents
• Occurrents occur in time; they are also
called perdurants.
• An occurrent is not wholly present at any
time less than its entire duration.
• Rather, it has temporal parts, which may
have different properties.
• But the occurrent itself does not undergo
change.
Examples
CONTINUANTS
OCCURRENTS
•
•
•
•
•
•
•
•
•
•
A person
An aircraft
An orchestra
A volcano
A heart
A life
A flight
A performance
An eruption
A heartbeat
Example: An Occurrent
• The first solo flight across the Atlantic.
• This is an occurrent (specifically: an event)
• It occurred over a 33-hour period in May
1927.
• Its temporal parts include the beginning (in
New York) and the end (in Paris).
• These properties are timeless: they cannot
change.
Example: A Continuant
• The Spirit of St Louis
• This is the aircraft in which Charles
Lindbergh completed the first solo flight
across the Atlantic.
• At each moment of the flight, the aircraft
was present – not just a part of it!
• At different moments, it had different
properties – e.g., its position, speed,
altitude. So, it underwent change.
Occurrents don’t change
• X changes if X has property P at time t1 and ~P
at time t2.
• Here, one and the same entity X has different
properties at different times.
• A temporally extended entity has temporal parts.
• If X has temporal parts X1 and X2, where X1 has
property P and X2 has ~P, then it is not the same
thing that has P earlier and ~P later.
• Hence differences between the temporal parts of
X do not constitute change in X.
But do events really not
change?
• ‘My life is becoming
harder’
• ‘Their lives moved
apart’
• ‘The battle grew
fiercer’
• ‘The protest became
violent’
In these cases what
changes is not an
event but a process
associated with an
event.
This solves nothing if
processes are, like
events, occurrents …
What is a process?
• Examples of processes, as I am using the
term, include:
– Human activities such as walking, swimming,
eating, drinking, driving a car, playing the
piano, pushing a barrow, peeling potatoes,
writing.
– Natural phenomena such as rainfall, ebb and
flow of the tide, photosynthesis, circulation of
the blood, flowing of a river, erosion and
deposition, rotation of the earth.
Some non-processes
• I do not include such things as the
‘process’ of making a pot of tea, making a
cake, preparing the index to a book,
refuelling a motor-car, or checking in at the
airport.
• These are closed routines consisting of a
definite sequence of actions or activities
leading to a specific end result.
• I shall call them structured actions.
Key properties of processes
• They are dissective: a period of time
occupied by a process can be divided into
subperiods each of which is occupied by
that process.
• They are open-ended: a process does not
have an intrinsic termination beyond which
it cannot continue.
Dissectivity
• The flow of the Thames through London: it
flowed throughout the twentieth century; it
flowed throughout 1988; it flowed
throughout March 1988; …
• If I walk for an hour, then the walking
process goes on during each subinterval
of that hour (even over intervals shorter
than a single step!)
Events are not dissective
• The conference takes place over the period 9th11th November.
• So it doesn’t take place on the 9th November, or
during the hour 2pm-3pm on that day.
• Parts of the conference took place on those
intervals, but not the whole conference.
• (Compare: ‘part/whole of the flow of the river’ –
these are spatial, not temporal!)
Open-endedness
Processes are open-ended:
• If I am walking, I can continue walking.
• If the river is flowing it can continue
flowing.
But events are not:
• If I run a mile, I cannot continue running it
(though I can start another one).
Can processes change?
• The flow of the river increases when the
snow melts.
• The heartbeat speeds up during exercise.
• The work became more diligent when the
supervisor arrived.
• The music became faster/louder/more
dissonant
• The protest became violent.
Can processes change?
• The grazing of the savannah became
more intense.
• The growth of the tree speeds up during
summer.
• The resurfacing work progressed from
north to south along the road.
• As the day continued, his driving became
more erratic.
Processes can change!
• In all these cases, we seem to have an
example of a process undergoing change.
• Occurrents, as described earlier, cannot
undergo change.
• So if we take the examples at face value,
processes are not occurrents.
• Which contradicts the universal assertion
that processes are occurrents.
SNAP and SPAN
• Two types of ontology, as advocated by Barry
Smith and collaborators.
• Grenon and Smith (2004): “A good ontology
must be capable of accounting for spatial reality
both synchronically (as it exists at a time) and
diachronically (as it unfolds through time)”.
• A SNAP ontology includes “all continuants
existing at some given instant of time” (a
SNAPshot).
• A SPAN ontology spans a succession of
instants, and contains entities extended over
such spans.
Mathematical time
• Instants correspond to real numbers,
intervals correspond to convex sets of real
numbers.
• The ‘flow’ of time arises from the ‘stitching
together’ of non-denumerably many
durationless instants.
• There is no change, only a static
ensemble of individually static snapshots.
Four running men?
“Snapshots” are misleading
• These “snapshots” are static.
• But the reality they portray is
dynamic.
• The world at an instant
comprises not just objects,
but also the processes in
which they are engaged.
• In real life (but not in the
pictures!) these processes
are directly observable.
Even these snapshots are
misleading!
• The snapshots are
static.
• The man-like figures
are not running (or
even moving).
• But even so, the
reality portrayed here
contains processes –
e.g., thermal motion
of atoms.
• The flow of time does not consist of a
succession of static snapshots.
• If it is built up from snapshots, they are
dynamic ones.
Motion: the most fundamental
process
• At time t, object a is at position p; at time t+d t, it
is at a different position q.
• Why is it in a different position at t+d t ?
• Because it is moving!
• But if “moving” means being in different positions
at different times, this explains nothing.
• We need the motion to be an ingredient of the
world at t if we are to invoke it to explain the
changes between t and t+d t.
Motion as an ingredient
• The physical description of the world at
time t includes not just objects but also
their momentum and kinetic energy –
these are real quantities which can be
transferred from body to body and which
are subject to conservation laws.
• Thus motion itself (and by extension, all
other processes) is part of the “furniture” of
the world.
What can we observe at t ?
• We see objects and matter.
• And processes (ongoing changes of
various kinds).
• We do not directly see events.
• To “see” an event we must make
observations over a period from
immediately before the event to
immediately after it.
So where do events come from?
• Events arise from processes in two main
ways:
– As ‘chunks’ of process: e.g., a bounded
episode of walking is a walk.
– As ‘boundaries’ of a process: e.g., the onset
or cessation of walking.
• Conversely, ‘higher-order’ processes can
arise from events, typically the openended repetition of some event type (e.g.,
the pulse, oscillations generally).
Processes from processes and
events from events
• Composition:
– Sequential. He ran there and back (a
composite event).
– Parallel. Walking and talking (a composite
process).
• Specialisation:
– He walked home specialises He went home.
– Walking with a limp specialises walking.
An Algebra of Processes and
Events
The various ways of deriving events/processes
from other events/processes can, in principle, be
formalised in an algebraic structure.
Are objects and processes distinct?
• Not always, or not always clearly so.
• A river can be regarded as an object or a
process.
• The river consists of water flowing
between banks. Both the water and the
flow are essential to its being a river.
• At time t, the water and its flow both exist;
but there is no event in sight.
Objects as processes
• A river can plausibly be described as a
process, without ontological impropriety.
• But there is no plausibility whatever in
describing a river as an event.
• This is true of many kinds of object, e.g.,
living organisms.
• I can see myself as a process (the process
of living my life), but not as an event.
Processes as continuants?
• Much of what we have said seems to
move processes closer to objects than
events:
– They are directly observable features of the
world at one time;
– They undergo change as time proceeds.
• This suggests that processes should be
regarded as continuants rather than
occurrents.
Experiential vs Historical
• Alternatively, we could set aside the
continuant/occurrent distinction and
replace it with something else.
• I favour the idea of a fundamental
distinction between
– experiential entities (the contents of a
“dynamic snapshot”: i.e., objects and
processes); and
– historical entities (summative records over a
sequence of snapshots: i.e., events)
The new picture
John Lyons (Semantics, 1977)
“The term … ‘historical’ is intended to suggest
the narration of events ordered in terms of
successivity and presented dispassionately with
the minimum of subjective involvement; and this
mode of description clearly relates to the static,
non-deictic, objective conception of time. The
term ‘experiential’, on the other hand, is
suggestive of the kind of description that might
be given by someone who is personally involved
in what he is describing; and this mode is no
less clearly related to the dynamic, deictic,
subjective conception of time.”
The Experiential Perspective (EXP)
• EXP relates to the world as experienced,
when it is present.
• The EXP world is constantly changing – it
is a world in flux.
• Conversely, whatever is changeable must
belong in EXP.
• Hence both objects and processes, which
are changeable, are EXP entities.
The Historical Perspective (HIST)
• HIST relates to the faits accomplis, the
historical record.
• It contains synoptic overviews that span a
succession of experiential ‘snapshots’.
• HIST entities are (mostly) extended in
time.
• They do not themselves change, but are
‘static’ configurations of changes that have
occurred.
SNAP / SPAN vs EXP / HIST
Properties of processes
• Processes, like objects, can be assigned
time-varying properties in the form
Property (process,time).
• These properties include things like speed,
intensity, periodicity – all of which are
possessed at individual times and can
vary over time.
Properties of events
• Events have properties such as
– Duration
– Time of occurrence
– Cause
– Outcome
– Structure
• These are all timeless properties that
attach to the event as an complete
individual.
Types and tokens
• In Property(process,time), the process is a
token, not a type, i.e., a process-individual
that has its own life-history distinct from
other individuals of the same type.
• The type of a process can be expressed
as a predicate applied to tokens, e.g.,
Running(john,p) & Active(p,t)
states that John is running at time t.
Specifying events
• Events can be specified internally or
externally.
– Internal: in terms of constituent processes by
which the event occurs.
– External: in terms of the net transition effected
by the event.
• Example:
– John took a walk (internal)
– John went to the station (external)
– John walked to the station (internal and
external)
Example: The Progressive
Aspect
• Problem: to represent the meaning of
– John is walking to the station
in a way that correctly captures its logical
relations with sentences such as
– John walked to the station
– John is walking
– John is at the station
1. Define ‘x walks to y’
WalkTo(x,y,e) =def
Walking(x,process(e)) & IsAt(x,y,result(e))
where
• process(e) is the constituent process of
event e.
• result(e) is the situation resulting from the
occurrence of e.
2. Define the progressive
For event type E,
ProgE(p) =def $e[E(e) & process(e)=p &
result(e)=goal(p)]
where goal(p) is the goal or end-point
towards which process p is directed.
John is walking to the station
Prog(WalkTo(john,station))(p)
 $e[WalkTo(john,station,e) & process(e)=p
& result(e)=goal(p)]
 $e[Walking(john,process(e)) &
IsAt(john,station,result(e)) & process(e)=p
& result(e)=goal(p)]
 Walking(john,p) &
IsAt(john,station,goal(p))
What have we done?
• We have analysed John is walking to the
station as meaning that John is walking
with the goal of being at the station.
• This is less trivial than it sounds!
• In particular, it depends on having a
formalism which does justice to the
difference in character between processes
and events.
The ‘Imperfective Paradox’
• John was walking to the station but he never got
there
$p $t [Past(t) &
Prog(WalkTo(john,station))(p) &
Active(p,t) &
~$e[WalkTo(john,station,e) &
Occurs(e) &
process(e)=p]]
This is not contradictory since Active(process(e),t)
does not imply Occurs(e).
Conclusions I
• Traditionally, continuants undergo change
but occurrents do not.
• Ordinary objects are good continuants and
events are good occurrents.
• But processes, usually regarded as
occurrents, none the less undergo change.
• On the other hand, they’re not exactly like
continuants either.
Conclusions II
• Motivated by this, we replace the
continuant/occurrent distinction (and
hence the SNAP/SPAN ontologies) by the
experiential/historical distinction.
• Objects and processes are experiential:
they are present in a (dynamic) snapshot
and evolve through time.
• Events are historical: they span a range of
times, synthesising a sequence of
changes into a unity.
Conclusions III
• Motivated by this, we advocate a
formalism which allows time-varying
properties to be predicated of experiential
entities, but not of historical ones.
• Our specific examples require an ontology
containing at least objects, processes,
events, situations, and times.
• Working this out in more detail is a
programme for future work …
THE END
Thank you for listening!