Temporal parts

In contemporary metaphysics, temporal parts are the parts of an object that exist in time. A temporal part would be something like "the first year of a person's life", or "all of a table from between 10:00 a.m. on June 21, 1994 to 11:00 p.m. on July 23, 1996". The term is used in the debate over the persistence of material objects. Objects typically have parts that exist in space—a human body, for example, has spatial parts like hands, feet, and legs. Some metaphysicians believe objects have temporal parts as well.

Originally it was argued that those who believe in temporal parts believe in perdurantism, that persisting objects are wholes composed entirely of temporal parts. This view was contrasted with endurantism, the claim that objects are wholly present at any one time (thus not having different temporal parts at different times). This claim is still commonplace, but philosophers like Ted Sider believe that even endurantists should accept temporal parts.

Not everyone was happy with the definition by analogy: some philosophers, such as Peter van Inwagen, argued that—even given the definition by analogy—they still had no real idea what a temporal part was meant to be (1981: 133), whilst others have felt that whether temporal parts existed or not is merely a verbal dispute (Eli Hirsch holds this view).

Gallois surveys some of the attempts to create a more specific definition (Gallois 1998: 256). The early attempts included identifying temporal parts with ordered pairs of times and objects, but it seems relatively unproblematic that temporal parts exist given the definition and ordered pairs seem unsuitable to play the role that perdurantists demand, such as being parts of persisting wholes—how can a set be a part of a material object? Later perdurantists identified persisting objects with events, and as events having temporal parts was not problematic (for example, the first and second halves of a football match), it was imagined that persisting objects could have temporal parts. There was a reluctance from many to identify objects with events, and this definition has long since fallen out of fashion.

Of the definitions closest to those commonly used in the literature, the earliest was Thomson:

x is a cross-sectional temporal part of y =df (∃T)[y and x exist through T & no part of x exists outside T & (∀t)(t is in T ⊃ (∀P)(y exactly occupies P at t ⊃ x exactly occupies P at t))] (Thomson 1983: 207).

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