A priori reflection, common sense, and intuition have proved unreliable sources of information about the world outside of us. So the justification for a theory of the categories must derive from the empirical support of the scientific theories whose descriptions it unifies and clarifies. We don?t have reliable information about the de re modal profiles of external things either because the overwhelming proportion of our knowledge of the external world is theoretical--knowledge by description rather than knowledge by acquaintance. This undermines the traditional idea that to be an object of category C is to be an object with such-and-such characteristic possibilities of combination. But this is no loss because de re modal thought lacks utility for creatures like us.