PARTS OF ANIMALS, I. i. 



some part of it is the " nature " of a living creature. 

 Hence on this score especially it should be the duty 

 of the student of Natural science to deal with Soul 

 in preference to matter, inasmuch as it is the Soul 

 that enables the matter to "be the nature " of an 

 animal (that is, potefitialli/, in the same way as a piece 

 of wood " is " a bed or a stool) rather than the matter 

 which enables the Soul to do so. 



In view of what we have just said, one may well ask 

 whether it is the business of Natural science to treat 

 of Soul in its entirety or of some part of it only ; 

 since if it must treat of Soul in its entirety (i.e. 

 including intellect) there will be no room left 

 for any other study beside Natural science — it ^vill 

 include even the objects that the intellect appre- 

 hends. For consider : wherever there is a pair 

 of interrelated things, such as sensation and the 

 objects of sensation, it is the business of one 

 science, and one only, to study them both. Now 

 intellect and the objects of the intellect are 

 such a pair ; hence, the same science will study 

 both of them, which means that there will be 

 nothing whatever left outside the purview of 

 Natural science. All the same, it may be that 

 it is neither Soul in its entirety that is the 

 source of motion, nor yet all its parts taken 

 together ; it may be that one part of Soul, (a), viz. 

 that which plants have, is the source of growth ; 

 another part, (6), the " sensory " part, is the source 

 of change"; and yet another part, (c), the source 

 of locomotion. That even this last cannot be the 

 intellectual part is proved, because animals other 

 than man have the power of locomotion, although 

 none of them has intellect. I take it, then, as evident 



71 



