The principle that a moving body must continue to move unless something stops it was not known to Aristotle nor even unconsciously assumed by him. The effect of this ignorance upon his philosophy was discussed in C.Q. 1939, p. 129 f. It forbade him to conceive of a mechanist theory in the nineteenth-century sense. It enabled him to hold, what must seem self-contradictory to us, that all events have definable causes without there being a universal nexus of causes and effects (future events, therefore, he thought of as not yet determined in the nature of things). And it compelled him to believe that nature could not be orderly unless guided by a purposive force. Therefore he attacked those scientists who had thought that the world could be explained in terms of the compulsions and interactions of natural stuffs—a principle which they vaguely called Necessity, Ananke. In attacking their doctrine A. cannot have thought he was attacking the mechanistic determinism which modern critics have detected in their words: for he could not even conceive of such an idea. There is an a fortiori case for arguing that his predecessors cannot have conceived of it either. But it is always possible that A. misunderstood them. And there is still Epicurus to consider.