 Returning now to Almost-Lewis’s fundamental ontology, the options seem to be these: It might be that a spacetime point (or sequence of points) instantiates a perfectly natural property (respectively, relation) by instantiating a universal, in the sense of Armstrong. It might be that it has it by having as one part a certain kind of trope, in roughly the sense of Williams. (Whence we must amend slightly, and take these tropes to be the fundamental entities.) It might be that it has it by belonging to a special sort of set of (actual and merely possible) spacetime points—special either on account of the resemblances that unite its members and distinguish them from non-members, or on account of simply being perfectly natural. Regardless of which one chooses, Lewis thinks, one’s theory of natural properties and relations ought to respect four philosophically-motivated constraints: