 Do these conceptions characterize the same class of properties? There are a number of different possibilities here, but one that has received some attention in the literature is that physical theory only tells us about the dispositional properties of physical objects, and so does not tell us about the categorical properties, if any, that they have — a thesis of this sort has been defended by a number of philosophers, among them Russell (1927), Armstrong (1968), Blackburn (1992) and Chalmers (1996). Hence, if physical objects do have categorical properties, those properties will not count as physical by the standards of the theory conception. On the other hand, there seems no reason not to count them as physical in some sense or other. If that is right, however, then the possibility emerges that the theory- and the object-conceptions characterize distinct classes of properties. 