Aristotle's teleology is a central component of his philosophy, and interpretations of it often heavily influence evaluations of the significance of his thought, both in science and in philosophy. Much has been written about this aspect of his philosophy, but surprisingly little sustained attention has been directed to what is clearly the fundamental question: what, precisely, does Aristotle mean when he asserts that something is, or comes to he, for the sake of something?

If we are to answer this question with both historical accuracy and philosophical precision, how must we proceed?

The place to begin, of course, is with the text – ideally, with Aristotle's own statement of an answer. One would expect to find, somewhere in the vast Aristotelian corpus, a thorough analysis and explicit definition of this central notion. Surprisingly, it is not there to be found. Readers of the corpus will search in vain for a detailed analysis of what it is to be (or come to be) for the sake of something.

The longest continuous passages on final causality, Physics 11.8 and (sections of) Parts of Animals 1.1, while containing much that eventually proves helpful, do not address themselves directly to this issue. In each case, the purpose is to argue for the applicability to nature of a conception of final causality whose precise meaning and statement is largely taken for granted.