REASON 



a theory to a particular case). In induction one starts from 

 observed data and develops a generalisation which explains the 

 relationships between the objects observed. On the other hand, in 

 deductive reasoning one starts from some general law and applies 

 it to a particular instance. Thus in deductive reasoning the derived 

 conclusion is contained within the original premiss, and should 

 be true if the premiss is true. 



Since deduction consists of applying general principles to further 

 instances, it cannot lead us to new generalisations and so cannot 

 give rise to major advances in science. On the other hand the 

 inductive process is at the same time less trustworthy but more 

 productive. It is more productive because it is a means of arriving 

 at new theories, but is less trustworthy because starting from a 

 collection of facts we can often infer several possible theories, all 

 of which cannot be true as some may be mutually incompatible ; 

 indeed none of them may be true. 



In biology every phenomenon and circumstance is so complex 

 and so poorly understood that premisses are not clear-cut and 

 hence reasoning is unreliable. Nature is often too subtle for our 

 reasoning. In mathematics, physics and chemistry the basic 

 premisses are more firmly established and the attendant circum- 

 stances can be more rigidly defined and controlled. Therefore 

 reason plays a rather more dominant part in extending knowledge 

 in these sciences. Nevertheless the mathematician Poincare said : 

 " Logic has very Httle to do with discovery or invention." Similar 

 views were expressed by Planck and Einstein (pp. 55, 57). The 

 point here is that inductions are usually arrived at not by the 

 mechanical application of logic but by intuition, and the course 

 of our thoughts is constantly guided by our personal judgment. 

 On the other hand the logician is not concerned with the way 

 the mind functions but with logical formulation. 



From his experience in finding that his hypotheses always had 

 to be abandoned or at least greatly modified Darwin learnt to 

 distrust deductive reasoning in the biological sciences. He said : 



" I must begin with a good body of facts, and not from 

 principle, in which I always suspect some fallacy."^* 



A basic difficulty in applying reason in research derives from 

 the fact that terms often cannot be defined accurately and 



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