 First, he offers an account of what the fundamental ontological structure of the world is. Is, and must be—although as we’ll see, that qualification turns out to be in a certain sense trivial. This account of fundamental ontology of course presupposes that the word “fundamental” means something, and in particular manages to cleanly distinguish a certain central core of one’s ontological commitments from the rest. Suppose these commitments take the form of views about what entities (or “particulars”) there are, and what properties and relations they stand in. Then we can distinguish two questions. Are some entities more fundamental than others—with, perhaps, an elite group of entities being the most fundamental? Are some properties/relations more fundamental than others—again, with, perhaps, an elite group being the most fundamental? You might find a “yes” answer to both questions attractive. (E.g., chairs exist, but they are not fundamental-level entities—though perhaps quarks are. Likewise, some chairs have the property of being made of oak; but this is not a fundamental-level property—though perhaps the property of having such-and-such electric charge is.) As for Lewis’s own views, with respect to the second question they are fairly unambiguous: He is quite clear that a proper ontology must include not just particulars but also properties and relations (see especially 1983b); he is equally clear that it is a perfectly objective and determinate matter which of these properties/relations are more fundamental (or, in his terminology, more “natural”) than others (ibid.); he is officially agnostic about whether some properties/relations are most fundamental, or perfectly natural (1986f). His views on the first question are, to my eyes at least, more difficult to discern—but for reasons that, in the final analysis, probably do not matter. See the