Lecture on Chapter 3 of Porphyry’s Introduction

Difference, however, is predicated in common, peculiarly, and most peculiarly. For one thing is said to differ from another in common, in consequence of differing in some respect or other, either from itself, or from something else. For Socrates differs from Plato, in being another person, and he differs from himself when a boy, and when he becomes a man, and when he does any thing, or ceases to do it. And Difference is always perceived in the various ways in which a thing is after a certain manner affected. But one thing is said to differ peculiarly from another, when one thing differs from another by an inseparable Accident…