144 THE UNIQUENESS OF LIFE 



another. This holds only when we are dealing with two 

 logical opposites, one of which must be true. Many times 

 over in the history of thought there has been a rebound 

 from mechanistic interpretation discovered to be inadequate, 

 and the rebound has almost always landed the inquirer in a 

 doctrine of positive vitalism, in the assumption that there 

 is some non-perceptual agency at work in a living body which 

 is not present in the inorganic domain, and without which 

 the results would be otherwise. We shall not jump to this 

 conclusion, but we must consider it carefully. In its clearest 

 form it asserts the actuality of a ' vital principle ', or ' vital 

 impulse ', or ' entelechy ', of a non-perceptual character, oc- 

 casionally operating in living creatures and operating direc- 

 tively. Is this a tenable theory? 



§ 2. The Problem: Vitalism or Mechanism, or Neither? 



Before we discuss the theories of vitalism, it may be use- 

 ful to refer to three preliminary considerations. 



{a) It is maintained by some that mechanistic formula- 

 tion {i.e., description in terms of matter and motion) is 

 not exhaustive even within the domain of the not-living. 

 It seems to be adequate for certain purposes, e.g., when the 

 navigator deals with the tides, but is it certain that it is 

 an ideal formulation for things in general? Does it take 

 account of everything, e.g., of the probability that the living 

 evolved from the not-living ? But the adequacy of mechanical 

 categories in the domain of the inorganic is a question for 

 expert physicists; it is not the biologist's business. Our 

 question is w^hether the formulae which work adequately, 

 if not exhaustively, in describing the not-living world, are 

 beginning to answer the distinctively biological problems. 

 If not, what alternatives are there ? 



