When a window shatters, what exactly has occurred? We naturally say something happened—but what kind of thing is a happening? The ontology of events raises surprisingly difficult questions about the basic furniture of reality. Events seem distinct from ordinary objects like tables and electrons, yet they play indispensable roles in our explanations of causation, change, and temporal experience.

Philosophers distinguish between continuants (entities that persist through time while remaining wholly present at each moment) and occurrents (entities that unfold through time, existing only partially at any given instant). This distinction carves reality at a fundamental joint. Objects endure; events happen. But what makes something an event rather than an object, and how do we determine when we have one event versus two?

These questions matter beyond academic metaphysics. Our theories of causation typically invoke events as relata—causes and effects are events, not objects. Our explanatory practices presuppose we can identify and individuate events. Getting the metaphysics wrong distorts our understanding of change itself.

Consider the difference between a cat and a purring. The cat persists through time, existing wholly at each moment of its life. It has spatial parts (tail, whiskers) but no temporal parts—the cat yesterday isn't a part of the cat, it simply is the cat at an earlier time. Philosophers call such entities continuants or endurants. They maintain their identity through change while remaining numerically identical across temporal intervals.

Events exhibit fundamentally different temporal structure. A purring unfolds through time, possessing genuine temporal parts. The first second of purring is literally a part of the whole purring, just as a hand is part of a body. Events are occurrents or perdurers—they extend through time rather than persisting through it. No temporal slice of an event constitutes the whole event.

This categorial distinction has profound implications. Objects can change their properties while remaining the same object—the cat grows, yet remains numerically identical. Events cannot change in this way. An event's properties are fixed by how it unfolds. The shattering cannot become louder midway through; rather, its latter temporal part is louder than its earlier part. Events have their temporal profiles essentially.

The continuant-occurrent distinction also matters for location. Objects have locations at times; events occupy spatiotemporal regions. When we ask where the explosion occurred, we specify both spatial and temporal boundaries. Events are four-dimensional entities in a way objects (on the standard endurantist view) are not. This difference shapes how events interact with spacetime structure and how they figure in physical theories.

Takeaway

Objects persist through time remaining wholly present at each moment, while events unfold through time with genuine temporal parts—a distinction that determines how entities relate to change, location, and identity.

Suppose someone signals by raising their arm. Is the signaling identical to the arm-raising, or are these distinct events? Coarse-grained theories, associated with Donald Davidson and W.V.O. Quine, individuate events spatiotemporally: events are identical when they occupy exactly the same spatiotemporal region. Since the signaling and the arm-raising coincide perfectly in space and time, they are one event under two descriptions.

Fine-grained theories, championed by Jaegwon Kim and Alvin Goldman, reject this identification. The signaling essentially involves communicative intent; the arm-raising does not. Since these events differ in their essential properties, they must be distinct—even if colocated. Fine-grained theorists multiply events: wherever coarse-grained theorists see one event diversely described, fine-grainers discern multiple coincident events.

The choice has significant consequences for causal explanation. If the signaling and arm-raising are identical, then whatever causes one causes the other. But this seems wrong—the muscle contraction causes the arm-raising, but does it cause the signaling? The signaling seems to require additional conditions (conventions, intentions) beyond mere arm movement. Fine-grained individuation preserves these causal distinctions.

Yet coarse-grained theories have advantages too. They avoid ontological proliferation and align with how physics describes reality—in terms of spatiotemporal happenings, not intention-laden events. The dispute reveals a tension between explanatory adequacy and ontological parsimony. Our intuitions about event identity pull in opposing directions, suggesting that event individuation may be partly conventional rather than fully determined by metaphysical facts.

Takeaway

Whether the arm-raising and the signaling count as one event or two depends on whether you individuate events by spatiotemporal location or by essential properties—and this choice ramifies through your entire theory of causation.

Jaegwon Kim proposed an influential fine-grained theory: events are property exemplifications. Formally, an event is an ordered triple [x, P, t]—object x exemplifying property P at time t. The shattering of window w at noon is the event [w, shattering, noon]. This structured conception makes event identity transparent: events are identical just when they involve the same object, same property, and same time.

Kim's theory elegantly explains why events have their constitutive properties essentially. The event [Brutus, stabbing-Caesar, t] could not have been a kissing, because then it would be a different triple entirely. Events on this view are type-individuated by their constituent properties. Change any element of the triple, and you have a numerically distinct event.

Critics raise several objections. First, Kim's theory may generate too many events. If Brutus stabs Caesar quickly, we have both [Brutus, stabbing-Caesar, t] and [Brutus, stabbing-Caesar-quickly, t]. Are these one event or two? Kim must say two, since different properties figure in the triples. But this seems to multiply events beyond necessity—surely the quick stabbing just is the stabbing, performed quickly.

Second, the theory faces questions about which properties generate events. Does every property exemplification constitute an event? When the table exemplifies being-three-feet-from-the-window at noon, is that an event? Kim's framework struggles to distinguish genuinely eventive properties from merely stative ones without importing further theoretical machinery. The elegance of the formal definition may obscure substantive questions about which property exemplifications deserve event status.

Takeaway

Kim's theory that events are property exemplifications provides precise identity conditions but faces pressure from both directions—generating too many events from property variations while struggling to exclude non-eventive property exemplifications.

Events constitute a distinctive metaphysical category—occurrents that unfold through time rather than persisting through it. This basic categorial status shapes how events figure in our theories of causation, explanation, and temporal experience.

The dispute between fine-grained and coarse-grained individuation reveals that event identity conditions remain genuinely contested. Kim's property exemplification theory offers formal precision but at costs some find unacceptable. No theory yet commands consensus.

What hangs on this? Our causal explanations presuppose event individuation. Getting clear on the metaphysics of events clarifies the foundations of explanatory practice itself—showing that abstract ontology connects intimately with how we understand the world's causal structure.