PHYSICS, BIOLOGY, AND PSYCHOLOGY. 137 



on the contrary, interprets biological phenomena in 

 terms of a special conception based on the observation 

 of life itself may be called the biological theory. 



Of these opposing theories each seeks to interpret 

 the same facts in its own way, and the one way is com- 

 pletely different from the other. But there is also an 

 intermediate theory — that known as vitalism. The 

 vitalists accept as true, so far as it goes, the physical 

 and chemical interpretation of the phenomena connected 

 with living organisms, but maintain that in living 

 organisms we must, in addition, assume the existence 

 of something quite distinct which interferes with and 

 guides the physical and chemical reactions. This some- 

 thing has been called " vital force," " the vital principle," 

 or, to use Driesch's expression, " entelechy." So long- 

 as the vitalists confine themselves to merely pointing 

 out the deficiencies of the purely mechanistic theory, 

 the evidence which they bring forward is so strong that 

 it seems "to me to be unanswerable. When, however, 

 they try to define vitalism on its positive side, the result 

 is quite indefinite. The something which was supposed 

 to interfere from without in the physical and chemical 

 reactions can always be shown by experiment to be 

 dependent on what were admitted to be physical and 

 chemical conditions, though there is no explanation of 

 how these conditions bring about the actual results. 

 Vitalism thus represents no clearly definable working 

 hypothesis, and for this reason I do not propose to con- 

 sider it further. Similar objections apply to the cor- 

 responding animistic theory in psychology. 



I shall now try to present shortly the mechanistic 

 argument, and what seem to me its fatally weak points. 



