 A more promising option is to reject the second premise of the argument, that co-specific or relevantly similar things like Socrates and Callias must have a common form. This one might reject if one were a believer in particular forms. The question of whether Aristotle’s forms are particular or universal has garnered a huge amount of scholarly attention (those in favour of particular forms include Sellars 1957, Frede 1978, and Irwin 1988; those in favour of universal forms include Albritton 1957, Lewis 1991, and Loux 1991). If Aristotle believed in universal forms, he could have constructed particular forms out of some kind of indexed version of the universal (e.g., an ordered pair of the universal form and the thing which had it); but that would make the identity of the particular form dependent on that of the substance that had it. Since it is the substance’s form which is acting as principle of individuation, if the common form premise is rejected, particular forms cannot be individuated by the substances that have them, on pain of circularity: what makes Socrates different from Callias is that they have different forms; and what makes their forms different is that one belongs to Socrates, the other to Callias. To play this role, particular forms would have to be defined independently of the things that have them. It would be a particular form which combines with a thing’s matter to make it the thing that it is. Some scholars find this conception of particular forms problematic.