PARTS OF ANIMALS, I. i. 



bronze or of iron. Now the body, like the hatchet, 

 is an instrument ; as well the whole body as each 

 of its parts has a purpose, for the sake of which it 

 is ; the body must therefore, of necessity, be such 

 and such, and made of such and such materials, 

 if that purpose is to be realized. 



It is, therefore, evident that of Causation there are 

 two modes ; and that in our treatise both of them 

 must be described, or at least an attempt must be 

 made to describe them ; and that those who fail 

 herein tell us practically nothing of any value about 

 " Nature," for a thing's " nature " is much more a 

 first principle (or " Cause ") than it is matter. (In- 

 deed, in some places even Empedocles, being led 

 and guided by Truth herself, stumbles upon this, 

 and is forced to assert that it is the logos which is a 

 thing's essence or nature." For instance, when he is 

 explaining what Bone is, he says not that it is any one 

 of the Elements,^ or any two, or three, or even all of 

 them, but that it is " the logos of the mixture " of 

 the Elements. And it is clear that he would explain 

 in the same way what Flesh and each of such parts is. 

 Now the reason why earlier thinkers did not arrive 

 at this method of procedure was that in their time 

 there was no notion of ** essence " and no way of 

 defining " being." The first to touch upon it was 

 Democritus ; and he did so, not because he thought 

 it necessary for the study of Nature, but because he 

 was carried away by the subject in hand and could 

 not avoid it." In Socrates' time an advance was 

 made so far as the method was concerned ; but at 

 that time philosophers gave up the study of Nature 



to he to you, is for you." Protagoras had emphasized the 

 validity of sense-data ; Democritus denied it. 



77 



