 Following Russell (1927), some philosophers suggest that physics tells us only about the ‘structural’ properties of things — such as their dispositions and nomic relations — rather than about the ‘intrinsic’ properties which supposedly underlie and account for their structural properties. Thus Daniel Stoljar (2001) argues that there are two distinct notions of the physical and correspondingly of physicalism, depending on whether one appeals only to what is provided for by physics or also to the intrinsic properties of physical objects. He suggests that even if one of the corresponding two versions of the conceivability argument is sound, the other is not — because (roughly) physicalists can always object that, since we do not know enough about the physical world (in particular, about its intrinsic properties), we cannot ‘strongly’ conceive of the possibility of zombies.