  Furthermore, if there are individual essences, two individuals, x and y, couldn’t differ only in their contingent properties. (I is an individual essence of x if and only if x has I in every possible world in which it exists and, for any individual, y, and any possible world, w, if y has I in w, y in w is identical with x.) For suppose they did. Then their essential properties would be the same. A being’s individual essence is an essential property of it, however. Hence, if x and y had the same essential properties, they would also have to have the same individual essence. But, in that case, x and y wouldn’t be two individuals contrary to our supposition. And if no two beings can differ only with respect to their contingent properties, two gods can’t either. (For a sophisticated version of an argument of this type see Zagzebski 1989.)