Temporal Parts
Sider (Ted)
Source: Sider (Ted), Hawthorne (John) & Zimmerman (Dean), Eds. - Contemporary Debates in Metaphysics
Paper - Abstract

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Author’s Introduction1

  1. I will argue that temporal parts theory is true, but first we need to get clear on what exactly this theory says. Let’s start with the idea that time is like space. Everyone has seen timelines, in magazines and encyclopedias. For some reason, time is easier to comprehend when represented by a spatial diagram. A timeline is such a diagram.
  2. Diagrams of motion from high school physics take this a step further, by representing one dimension of space in addition to time. Since the diagram contains only a single spatial axis, it can represent only one spatial dimension of the particle’s motion (motion in the x direction).
  3. Space-time diagrams take this a step further, by representing more spatial dimensions alongside time.
  4. All these diagrams represent time as just another dimension, alongside the spatial dimensions. Given how convenient this method of representation is, many philosophers and scientists have wondered whether time itself is in some sense just another dimension. The question amounts to whether, and to what extent, time is like space.
  5. Temporal parts theory is the claim that time is like space in one particular respect, namely, with respect to parts. First think about parts in space. A spatially extended object such as a person has spatial parts: her head, arms, etc. Likewise, according to temporal parts theory, a temporally extended object has temporal parts. Following the analogy, since spatial parts are smaller than the whole object in spatial dimensions, temporal parts are smaller than the whole object in the temporal dimension. They are shorter-lived. The spacetime diagram makes this clear. The whole person is ... spread out from left to right because he lasts over time ...
  6. A person’s temporal part at a time is exactly the same, spatially, as the person at that time, but it exists only for a moment.
  7. Temporal parts have spatial parts, and spatial parts have temporal parts.
  8. The existence of temporal parts is just one way that I believe time to be like space. Here are two others (the nature of time is discussed more fully in chapter 5).
    1. Time is like space regarding the reality of distant objects. Spatially distant objects, such as objects on Mars, are just as real as objects here on Earth. Likewise, I think, temporally distant objects, such as dinosaurs, are just as real as objects we experience now. The belief that temporally distant objects are real is sometimes called “eternalism”. (The main opposing view, “presentism”, says that only objects in the present time exist.)
    2. Time is like space regarding the relativity of here and now. There is no one true here. I think that the word ‘now’ works analogously. The combination of this theory of the function of ‘now’ and eternalism is often called the “B-theory of time”.
  9. It is important to distinguish between the different facets of the space-time analogy, since some philosophers accept some facets while rejecting others. Some accept the B-theory while denying the existence of temporal parts; and some embrace temporal parts while denying that time is like space in one or more ways. What I will defend here, however, is the “B-theory” version of temporal parts theory.
  10. So: is temporal parts theory true? Do temporal parts really exist — do persons and other physical objects really have parts that last only for an instant? Temporal parts theory is a very general and speculative theory about the world, about what objects exist and what they are like. It is speculative because the question of its truth is hard to settle by observation or experiment. Crudely put, objects look the same, whether or not they are made of temporal parts. Experiment and observation would be unnecessary if all rival theories were internally inconsistent; then we could deduce temporal parts theory from pure logic alone. Unfortunately this is not the case; there are internally consistent opposing theories.
  11. We cannot prove temporal parts theory, but never fear! I believe that assessing the philosophical case for temporal parts allows one to make a decent educated guess. I will consider the following arguments for temporal parts:
    1. the problem of change,
    2. the paradoxes of material constitution, and
    3. the argument from vagueness and anthropocentrism.


See Sider: Temporal Parts.

In-Page Footnotes

Footnote 1: Truncated rather arbitrarily, with diagrams and examples removed!

Text Colour Conventions (see disclaimer)

  1. Blue: Text by me; © Theo Todman, 2019
  2. Mauve: Text by correspondent(s) or other author(s); © the author(s)

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