ARISTOTLE'S BIOLOGY 



of an animal or its parts: a dead body is not 

 a man, nor a bronze hand a hand, nor the eye 

 in a dead body really an eye. Rather, to de- 

 scribe an animal, one must show what it 

 actually is in substance as well as form; and 

 so with its several organs. He then argues 

 that it is the soul or life which constitutes the 

 essential nature of the animal. For " nature 

 is spoken of in two senses, and the nature of a 

 thing is either its matter or its essence; nature 

 as essence including both the motor cause and 

 the final cause. Now it is in the latter of 

 these two senses that either the whole soul 

 or some part of it constitutes the nature of an 

 animal." 



Nature always seeks an end, — a famous 

 Aristotelian statement; and the end is the final 

 cause, which in the case of animals is the soul 

 or the life of the animal, the full functioning 

 of its nature. Logically, that is, in thought, 

 this final cause or end is prior to the motor 

 cause; " For this is the Reason, and the Reason 

 forms the starting point, alike in the works 

 of art and in works of nature." With a builder 

 the final cause is the construction of a house; 

 in nature it is the making of an animal. " In 

 the works of nature the good end and the final 



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