My aim in what follows is to explain and to motivate a theory of essence, existence and individuation that I think is to be found in the later and more advanced of the extant writings of Aristotle. The view to be explored has several features that are noteworthy from a scientific as well as a philosophical standpoint: it centers especially, though not exclusively, on a concept of what an individual material object is – a concept that has both intrinsic interest and (if some suggestions I shall advance as to its provenance and motivation are accepted) a historical significance that has not always been accurately appreciated.

The subject has of course had a great many discussants over the millennia, and so inevitably there is overlap at most points here with what others have had to say. Yet anyone familiar with the richness, elusiveness and originality of Aristotle's thought in this area will readily agree that present understanding of it remains imperfect and that new points and perspectives regarding it are still to be gained; the topic is limitless. Such novelties of content as I shall recommend will emerge in their due order. But there are also some unconventional and very likely exceptionable aspects to my method in this study which should be identified at once.

One is a variation on the usual approach to a historical philosopher – that of working from his text to his meaning. For my interpretive practice here is in places frankly reconstructive in character, synthetic rather than analytic; where it seems needed, or even merely helpful, I do not stick at approaching the text by convergence, rather than by trying to extract doctrine from it in the conventional way.