Parts can have parts

Words denoting wholes bear the has-relation to the labels for their parts, but the parts can, in turn, have parts, and a whole can be a part of a larger whole, as illustrated in Figure 3.1.

I have not posited an inverse relation to the has-relation, one that would guarantee the existence of the relevant larger whole whenever a part of it is present. This is because parts can exist in the absence of the larger whole: for instance, newly-cast or hewn kerb stones can be lying around and not be part of any street; a builders’ merchant keeps stocks of windows for houses that have not yet been built. Furthermore, the same kind of part can belong to different kinds of whole, a given kerb need not be part of a street; it could be part of an off-street parking lot.