ARISTOTELIAN PHYSICS. 47 



Cause and Effect ; and so far as the Aristotelian phi- 

 losophy reasons from these assumptions, it has a 

 real foundation, though even in this case the con- 

 clusions are often insecure. We have an example 

 of this reasoning in the eighth Book 7 , where he 

 proves that there never was a time in which change 

 and motion did not exist ; " For if all things were 

 at rest, the first motion must have been produced 

 by some change in some of these things ; that is, 

 there must have been a change before the first 

 change;" and again, "How can before and after 

 apply when time is not ? or how can time be when 

 motion is not ? If," he adds, " time is a numeration 

 of motion, and if time be eternal, motion must be 

 eternal." But he sometimes introduces principles of 

 a more arbitrary character ; and besides the general 

 relations of thought, takes for granted the inven- 

 tions of previous speculators ; such, for instance, as 

 the then commonly received opinions concerning 

 the frame of the world. From the assertion that 

 motion is eternal, proved in the manner just stated, 

 Aristotle proceeds by a curious train of reasoning, 

 to identify this eternal motion with the diurnal 

 motion of the heavens. " There must," he says, " be 

 something which is the First Mover 8 :" this follows 

 from the relation of causes and effects. Again^ 

 "motion must go on constantly, and, therefore, 

 must be either continuous or successive. Now what 



7 Physic. Ausc. viii. '1. p. 251. 



8 Physic. Ausc. viii. 6. p. 258. 



