and explained the basis on which it yields certainty, resolving all the objections raised against it. We have also discussed Alexander’s method in this matter—I mean the one he adopted in his book entitled Principles. He is thought to have departed from Aristotle’s method in favour of another, though it is drawn from principles established by Aristotle. Both methods are sound, but Aristotle’s is generally the more natural method.”

He said:

“However, in my view, if the method based on the Necessary Existent is rigorously formulated as I shall describe, it is valid, although it contains generalities requiring elaboration: it must be preceded by knowledge of the classes of things whose existence in substance is contingent, and of the classes of things whose existence in substance is necessary.

“This method consists in saying that whatever has contingent existence as a corporeal substance must be preceded by something whose existence as a corporeal substance is necessary. Whatever has necessary existence as a corporeal substance must, in turn, be preceded by that whose existence is necessary without qualification. This is that which has no potentiality whatsoever, whether in substance or in any of the other kinds of motion. Whatever is of this nature is not a body.

“For example, it may be apparent from the condition of the celestial body that its existence as a corporeal substance is necessary; otherwise, there would have to be a body prior to it. It is also apparent that it