In this paper I want to explore the application of some of Aristotle's central metaphysical notions to the analysis of living things. Commentators have often remarked that the conceptual pairs of matter / form and potentiality/actuality apply best to the analysis of Aristotle's favorite example, the bronze statue, but fit organic creatures – the true substances – less well. Two distinct problems arise for these more complex cases.

First, it seems impossible to point to something which serves as both matter ‘for’ and matter ‘of’ a living creature, as bronze does for statues. In Physics 1.7 Aristotle tells us that in any change some underlying thing or substratum persists, and it is easy to see that the bronze persists when a statue is molded, the gold continues in the bangle, etc. But what exists before a person, duck, or oak tree comes to be is an embryo, egg, or acorn (cf. Ph. 1.7 190b3–5) – and these surely do not remain in the finished creatures as their matter. This disanalogy is the target of William Charlton's criticism in his commentary on Physics 1 and II: