Peter Lupu makes the following objection to my claim that there are no substantive theses of metaphysics. Claims such as “there are no universals” are substantive metaphysical theses. But it is also a substantive thesis of nominalism, one which I (as a card-carrying nominalist) would surely uphold. The choice is mine!
I reply: is the thesis that there are no such things as ghosts, a substantive thesis in the theory of ghosts? No. Because it is not a thesis about ghosts. Any thesis in the theory of ghosts is about ghosts. But the thesis that there are no ghosts is a substantive theory not about ghosts, but about the world. Namely, that the world contains no ghosts. Not being a thesis about ghosts, it is not part of the theory of ghosts.
Analogously, the nominalist holds that there are no universals. His thesis is a substantive one, to be sure. But it is not part of the theory of universals. Rather, it is a substantive part of the theory of the world, that it contains no such things as ‘universals’.