PARTS OF ANIMALS, I. i. 



the individual from which the seed comes is the 

 source and the efficient agent of that Avhich comes 

 out of the seed. The reason is, that these things 

 are so arranged by Nature ; at any rate, the offspring 

 grows " out of the seed. Nevertheless, logically 

 prior to the seed stands that of which it is the seed, 

 because the End is an actual thing, and the seed is 

 but a formative process. But further, prior to both 

 of them stands the creature out of Λvhich the seed 

 comes. (Note that a seed is the seed "of" some- 

 thing in two senses — two quite distinct senses : it 

 is the seed " of" that out of which it came — e.g. a 

 horse — as well as " of " that Avhich will arise out of 

 itself- — e.g. a mule). Again, the seed is something 

 by potentiality , and Ave know Avhat is the relation of 

 potentiality to actuality.* 



We have, then, these tAvo causes before us, to wit, 

 the " Final " cause, and also Necessity, for many 

 things come into being owing to Necessity. Per- 

 haps one might ask which " Necessity " is meant 

 when it is specified as a cause, since here it can be 

 neither of the two modes which are defined in 

 the treatises AVTitten in the philosophical manner." 

 There is, howe\'er, a third mode of Necessity : it 

 is seen in the things that pass through a process of 

 formation ; as when we say that nourishment is 

 necessary, we mean " necessary " in neither of 

 the former two modes, but we mean that without 

 nourishment no animal can be. This is, practically, 

 "conditional" Necessity. Take an illustration: A 

 hatchet, in order to split wood, must, of necessity, be 

 hard ; if so, then it must, of necessity, be made of 



1015 a 20 fF.). The third he has referred to already at 

 639 b 2.0. viz. " conditional " necessity. See pp. 21 f. 



75 



