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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.

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On what goes on the ontology of processes and events

On What Goes On:The Ontology of Processes and Events

Antony Galton

University of Exeter, UK

How are processes related to events
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 5 th edition 1964
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 8 th edition 1990
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.


  • 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 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.



A person

An aircraft

An orchestra

A volcano

A heart


A life

A flight

A performance

An eruption

A heartbeat


Example an occurrent
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
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
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 …

But do events really not change?

What is a process
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
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
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.


  • 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
Events are not dissective

  • The conference takes place over the period 9th-11th 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
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 change1
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
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
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.

Snapshots are misleading
“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
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.

Motion the most fundamental process
Motion: the most fundamental process snapshots.

  • 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
Motion as an ingredient snapshots.

  • 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
What can we observe at snapshots.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
So where do events come from? snapshots.

  • 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 open-ended repetition of some event type (e.g., the pulse, oscillations generally).

Processes from processes and events from events
Processes from processes and events from events snapshots.

  • 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
An Algebra of Processes and Events snapshots.

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
Are objects and processes distinct? snapshots.

  • 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
Objects as processes snapshots.

  • 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
Processes as continuants? snapshots.

  • 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
Experiential snapshots.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
The new picture snapshots.

John lyons semantics 1977
John Lyons ( snapshots.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
The Experiential Perspective (EXP) snapshots.

  • 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
The Historical Perspective (HIST) snapshots.

  • 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.

Properties of processes
Properties of processes snapshots.

  • 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
Properties of events snapshots.

  • 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
Types and tokens snapshots.

  • 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
Specifying events snapshots.

  • 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
Example: The Progressive Aspect snapshots.

  • 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
1. Define ‘ snapshots.x walks to y’

WalkTo(x,y,e) =def

Walking(x,process(e)) & IsAt(x,y,result(e))


  • process(e) is the constituent process of event e.

  • result(e) is the situation resulting from the occurrence of e.

2 define the progressive
2. Define the progressive snapshots.

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
John is walking to the station snapshots.


  • $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
What have we done? snapshots.

  • 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
The ‘Imperfective Paradox’ snapshots.

  • 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) &


    This is not contradictory since Active(process(e),t) does not imply Occurs(e).

Conclusions i
Conclusions I snapshots.

  • 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
Conclusions II snapshots.

  • 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
Conclusions III snapshots.

  • 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

THE END snapshots.

Thank you for listening!