The chief difficulty that final causes present to modern philosophers lies in reconciling them with what Aristotle calls ‘necessity’, that is the automatic interactions of the physical elements. It is difficult to see, first, how laws of nature can be directed towards goals and still remain ‘necessary’; and, secondly, what could be the author and the means of such direction. The modern cybernetic model, and the concept of elaborate genetic coding, have not altered the problem; they have merely shown that some apparently teleological processes may in fact be necessary outcomes. It is arguable, as we shall see, that in the GA Aristotle himself was moving towards such a position. But there is no sign of it in PA, nor is there any sign in his writings generally that the relationship between finality and necessity could be a difficulty of the sort that we feel.

The novelty in Aristotle's theory was his insistence that finality is within nature: it is part of the natural process, not imposed upon it by an independent agent like Plato's world soul or Demiourgos. This is what allows him to claim that none of his predecessors had recognized the final cause with any clarity. Anaxagoras called his primary cosmological cause ‘Mind’, and for this Aristotle likened him to a lone sober man among drunks; Plato offered cosmic teleological causes in the Timaeus, Philebus and Laws; Xenophon argued for the popular belief in providential guidance of natural phenomena.