Mereology: A Philosophical Introduction

We could claim instead that the piece of wood is a proper part of the table, but that the table is not a proper part of the wood.

The reason to distinguish between the table and the piece of wood (and to avoid taking the first way out) is presumably that the table is a richer entity, one that instantiates some further properties (for example, some stylistic features—it is in the Art Nouveau style) that the piece of wood lacks.

Once their spatiotemporal coincidence is not taken as decisive evidence that they are identical, it is not clear either whether it serves as evidence that there is a mereological relation between them.

The very circumstance that they (allegedly) occupy the same region of space, are distinct, but are not in one another could suggest that the table and the piece of wood belong to different kinds, and that in general pieces of material (such as the piece of wood) and artifacts (such as the table) belong to different kinds.

Once this person denies Locke’s thesis, she might wonder if there is a mereological relation between the table and the piece of wood; and if she answers this question affirmatively, then she might wish to maintain that they are part of one another and yet different

This principle is denied by the person who thinks that the table and the piece of wood are different and colocated.

The principle according to which it is not possible for two distinct individuals to occupy one and the same region of space at the same time is usually called Locke’s thesis

In the so-called theory of constitution, there would be cases—we will discuss them in —in which two numerically different things are mutual parts.

The only case in which x and y are admitted as mutual parts is the case in which they are the same thing. But if x is a proper part of y, then x is not identical to y, and mutual proper parthood is ruled out.

PP is not merely antisymmetric, but asymmetric