Events

Events constitute a separate category of spatiotemporal objects which is different from the category of things. The main difference between events and things lies in their different ways of existing in time. Things, according to the common intuition, persist in time, while events happen, occur, or take place. Things are continuants, while events are occurents. This difference can be explained as follows. Compare the battle of Waterloo, which is an event, with Napoleon, a thing. Both Napoleon and the battle of Waterloo coexisted during a certain period of time, but at each moment of the battle Napoleon was fully present, while only a small part of the battle takes place at a given moment. Events are not repeatable – they occur as a whole only once – but things exist at different times without losing their identity. (It has to be added though that there are non-standard conceptions of how things persist in time, according to which at a given moment of time only a part of the thing is present, exactly as in the case of events. We will talk more about this later.)

Events are ubiquitous in natural language, as well as in the language of philosophy and of science. We talk without hesitation about battles, treaties, births, deaths, weddings, earthquakes etc. In philosophy events are typically considered as arguments of the causal relation. It is also common to talk about mental events. In physics events of coincidence play an important role in relativity theory, while measurements constitute the foundation of quantum mechanics. It is difficult to imagine a language which would not make reference to events. And yet some philosophers deny that events exist as a separate category of entities. To counter this claim, Donald Davidson has suggested a linguistic argument in support of the admission of events into one’s ontology. Consider the following sentence: (1) Jones slowly buttered a piece of toast with a knife in the kitchen at midnight. It is quite obvious that from this sentence we can logically derive several consequences, for instance that Jones buttered a piece of toast, that Jones buttered a piece of toast at midnight, or that Jones did something with a knife in the kitchen at midnight. And yet it is extremely difficult to formalise these valid inferences within standard first-order logic when we assume that the variables of our language range over things only. For example, the statement “Jones walked slowly” is formalised as P(a), where P represents the complex predicate “walks slowly” and a stands for the name “Jones”. But this method of interpretation treats the sentence “Jones walked” as containing a new predicate “walks” (Q) different from the adverbially modified expression “walks slowly”, and therefore cannot account for the unquestionable entailment between the two sentences (formula Q(a) cannot be logically derived from P(a)).

Davidson suggests that we should rephrase the above sentences in a language containing reference to events. The initial sentence (1) can be interpreted as follows: “There is an x such that x is a buttering of a piece of toast, x is done by Jones, x is done slowly, x is done with a knife, x is done in the kitchen, x is done at midnight”. By eliminating some elements of the multiple conjunction we can easily obtain required logical consequences, such as “There is an x such that x is a buttering of a piece of toast, and x is done by Jones” (“Jones buttered a piece of toast”), or “There is an x such that x is done by Jones, x is done with a knife, x is done in the kitchen and x is done at midnight” (“Jones did something with a knife in the kitchen at midnight”).

Accepting events as part of our ontology requires that we be able to give some criteria of identity and difference for them. When are two events numerically identical? One possible answer may be that the sufficient and necessary condition for the identity of events is their spatiotemporal coincidence. But there are convincing examples of numerically distinct events which nevertheless coincide in space and time. A typical example is that of a metal sphere which simultaneously rotates around its axis and heats up. The events of rotating and of heating up are clearly numerically distinct, and yet they occupy the same region of spacetime. One way of saving this intuition is to adopt Davidson’s causal criterion of identity: events x and y are numerically identical iff x and y have the same causes and the same effects. Clearly the rotation of the sphere and its heating up have different causes, and different effects (for instance the former causes the sphere to flatten a bit due to the centrifugal forces, while the latter causes it to expand uniformly). But there is one big problem with Davidsonian criterion – it is namely circular. Let us suppose that we have events x and y of which we don’t know yet whether they are identical or distinct, and let us suppose that x is caused by another event u, while y is caused by w. For simplicity’s sake we assume that x and y don’t stand in causal relation to any other events. Now, in order to decide whether x = y, we have to verify whether their causes u and w are one or two events. But to do that we have to apply Davidson’s criterion again, and this requires that we know whether x and y are identical (as they are effects of u and w). Here the circle closes, and apparently we have no way of solving our initial problem.

However, it turns out that under certain assumptions it is actually possible to decide in each case the issue of identity for a group of events using Davidson’s criterion. Here I follow the suggestion made by Leon Horsten. Suppose that we have a graph containing points representing descriptions of events (not events themselves!) and arrows representing causal relation. Moreover, let us assume that our graph satisfies the condition of completeness, i.e. for each pair of events e and e’, if e is a cause of e’, then each description of e is connected by an arrow with each description of e’. Under this assumption it turns out that each graph satisfying Davidson’s criterion is solvable, i.e. for each two descriptions it is decidable whether they refer to one or two distinct events. However, it may be pointed out that the assumption of completeness is too strong (if a graph is complete, this fact by itself already fixes some identity relations). A more reasonable assumption is that of semi-completeness: for all events e and e’, if e is a cause of e’, then each description of e is connected by an arrow with some description of e’. But it can be showed that semi-complete graphs are not always solvable, and therefore the problem of circularity remains.

Jaegwon Kim proposed a different interpretation of events as property exemplifications. More specifically, an event for Kim is a triple <a, P, t>; where a is an object, P is a property, and t is a time at which a possesses P. From this definition it follows that two events are identical iff they happen on the same object, at the same time, and they involve the same property. The last requirement ensures that the rotation and the heating of the sphere are numerically distinct. But Kim’s conception has several controversial consequences. First of all, it multiplies events beyond what is ordinarily acceptable. If Jones is walking slowly, his walking and his walking slowly constitute two distinct events (actually, there are as many different events of walking involved as there are ways to describe the individual style of Jones’ walking). This fact can actually threaten the analysis of logical inferences proposed by Davidson and sketched above, as in each sentence we are talking about a different event. Moreover, according to Kim’s approach it is an essential feature of an event that it occurs on a given object, at a given time, and that it involves a given property. From this it follows that my lecture on ontology given on Wednesday, February 17, at 11:30 could not have been given by someone else, could not have been a rock concert, and could not have started five minutes later. Especially the last consequence seems to be rather controversial. Other criticism of Kim’s conception is based on the observation that events can involve more than one object (relational events) or no object at all (spontaneous excitations of vacuum predicted in quantum field theory).

Event-ontologies are based on the assumption that events are the fundamental kind of objects and that other categories of objects can be reduced to events. According to one type of event-ontology, things are just sequences of events. A person, for instance, is a collection of all events from his/her birth to the death. It is worth noticing that such a reductive definition cannot be accepted by Kim, for in his conceptions events are defined in terms of things, so there would be obvious circularity. Alternatively, we could interpret events as consisting of properties and moment of time only, or we could rely on Davidson’s criterion, provided that its own circularity problem could be overcome.

Readings:

E.J. Lowe, Chapter 12 "Actions and events", pp. 214-231, A Survey of Metaphysics.
M.J. Loux, "Facts, states of affairs, and events", pp. 142-150, Metaphysics. A Contemporary Introduction.