Historical Dictionary of Metaphysics

Categories are of explanatory value in metaphysics partly because a category is an essential kind: a kind such that, necessarily, whatever belongs to it belongs to it essentially.

However, a nonspatial spirit or soul would be a concrete entity of an atypical sort that lacks spatial or temporal parts.

(D1) x is a concrete entity = df. x belongs to an ontological category (at Level C) that has among its possible instances entities having spatial or temporal parts,6 and (D2) x is an abstract entity = df. x is not a concrete entity

It is an interesting question when a kind is too specific to count as an ontological category.

Subdivisions of the category of substance (at Level D) might include physical object and spirit, subdivisions of boundary might include surface and edge, and so on.

Pairs, trios, and quartets of substances of which those substances are parts are collections (within mereology, or the theory of parts, one calls a collection of this kind a mereological sum or fusion).

Holes, shadows, and gaps are absences (also known as privations).

Surfaces, edges, and corners are boundaries (also known as limits).

Instants and durations are times.

Extended spatial regions and points are places.