 Returning, then, to those beings that are not-present in other beings, Aristotle thinks that in addition to primary substances, which are particulars, there are secondary substances, which are universals (2a11-a18). His example of such an entity is man (1a21), which, according to the present interpretation, is a universal in the category of substance. If we again accept the distinctions in question as I have drawn them, we should interpret secondary substances as essential characteristics of primary substances. Moreover, because primary substances seem to be members of natural kinds, it is natural to interpret secondary substances as the kinds to which primary substances belong. If that is so, then Aristotle thinks that not only are primary substances members of natural kinds but that they are essentially characterized by the kinds to which they belong.