 A is per se3 iff ‘A’ indicates ‘a this’ (tode ti), i.e., ‘A’ refers to just what A is. At Post. An.  i.22, Aristotle identifies the per se3 with substance, the rock bottom of a syllogistic chain. However, one might well ask whether there must be an analogous notion within a science. If so, A would be per se3 if A is a basic entity in a given science, an instance of the kind studied by the science. If so, the per se3 items in arithmetic would be units.