Similarly, rational activity is what makes a man to be a man and distinguishes him from a brute animal. 

 Gottfried Wilhelm Leibniz, a 17th-century German philosopher and mathematician,
 called his monads (the ultimate reality of material beings) entelechies in virtue of their inner self-determined activity. The term was revived around the turn of the 20th
century by Hans Driesch, a German biologist and philosopher, in connection with his vitalistic biology to denote an internal perfecting principle which, he supposed, exists in all living organisms.
ENCYCLOPÆDIA BRITANNICA          

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