Life

(Greek zoe; Latin vita; French La vie, German Das Leben; vital 
principle; Greek psyche; Latin anima, vis vitalis, German 
leberzskraft). 

The enigma of life is still one of the two or three most difficult 
problems that face both scientist and philosopher, and 
notwithstanding the progress of knowledge during the past twenty-
three hundred years we do not seem to have advanced appreciably 
beyond the position of Aristotle in regard to the main issue. What 
are its characteristic manifestations? What are its chief forms? 
What is the inner nature of the source of vital activity? How has 
life arisen? Such are among the chief questions which present 
themselves with regard to this subject. 

I. HISTORY

A. Greek Period 

The early Greek philosophers for the most part looked on movement 
as the most essential characteristic of life, different schools 
advocating different material elements as the ultimate principle 
of life. For Democritus and most of the Atomists it was a sort of 
subtle fire. For Diogenes it was a form of air. Hippo derives it 
from water. Others compound it of all the elements, whilst some of 
the Pythagoreans explain it as a harmony -- foreshadowing modern 
mechanical theories. Aristotle caustically remarks that all the 
elements except earth had obtained a vote. With him genuine 
scientific and philosophic treatment of the subject begins, and 
the position to which he advanced it is among the finest evidences 
of both his encyclopedic knowledge and his metaphysical genius. 
His chief discussions of the topic are to be found in his peri