ristotle's argument in Physics book viii; turn back to Readings, p.90, R.H. side (van den Bergh, p. 261), and re-read Averroes' summary of this argument. The third way is about possibility and necessity, and the key premise is that if something is possible then at some time that possibility must be realised; so if all things are such that their non-existence is possible, then at some time nothing will exist. This notion of "possible" as meaning "actual at some time or other" comes from Aristotle. It would seem that the third argument needs some patching. In a given finite period of time a possibility need not be realised: that my death is possible means, according to Aristotle, that it must happen sometime; but it hasn't happened yet. The third way seems to be a reductio ad absurdum: Suppose that there are only contingent beings, i.e. beings capable of ceasing to exist; and suppose this contingent universe has existed from eternity, i.e., that it has already existed through an infinite time. Then by now all possibilities must have occurred, including the simultaneous non-existence of everything. The fourth argument, from grades of being, is Platonic; it should remind you of Anselm's argument in Monologion, chapter 4, Readings, p.22. The fifth is like the argument from design, except that the evidence offered for the existence of an intelligence behind the universe is not the orderliness of the whole universe, but the apparently purposive activity of each and every part. Recall Aristotle's teleological view of nature, that a natural process is for the sake of some end. Aristotle's God did not appoint the ends, they just were! But Thomas Aquinas says that there can't be purposiveness without a guiding intelligence. ...
