 In response, it might be thought that subatomic particles are entirely characterised in terms of dispositions like spin and electric charge, and therefore that they possess no categorical properties on which their dispositions would supervene, in which case the possibility of grounding via supervenient structure is blocked. Williams (2009, p. 13) retorts, though, that the reason why physicists speak only in terms of dispositions when they describe subatomic particles is merely that the only means they have to investigate subatomic particles is to ‘poke and prod at them with bombardments, and see how they react’ (For a similar point, see Strawson 1980; Blackburn 1990; Jackson 1998; Langton 1998; Hawthorne 2002; Lewis 2009). But this is not to say that they, as a matter of fact, have no categorical properties at all. In fact, we have, Williams continues to argue, good metaphysical reasons for attributing categorical properties to subatomic particles.