224 THEORIES AND MODELS 



The Jiypothetico-deductive method. Induction is a bipartite proc- 

 ess accurately, if excruciatingly, described by the barbarism of the 

 section heading. Certain items of experience that somehow disturb 

 him spur the scientist to invent new hypotheses. Each of these he 

 evaluates by discovering whether, by deduction from it, he can in- 

 deed account for the items of experience from which he first took 

 departure. We have then first an act of creation, of some tentative 

 hypothesis, at once followed (and probably overlapped) by an act 

 of appraisal. The first (inductive) creative flight and the second 

 more prosaic ( deductive ) descent proceed, says Whewell, along the 

 same stairway: 



But still there is a great difference in the character of their move- 

 ments. Deduction descends steadily and methodically, step by step: 

 Induction mounts by a leap which is out of the reach of method. She 

 bounds to the top of the stair at once; and then it is the business of 

 Deduction, by trying each step in order, to establish the solidity of her 

 companion's footing. Yet these must be processes of the same mind. 

 The Inductive Intellect makes an assertion which is subsequently 

 justified by demonstration; and it shows its sagacity, its peculiar char- 

 acter, by enunciating the proposition when as yet the demonstration 

 does not exist: but then it shows that it is sagacity, by also producing 

 the demonstration. 



The historian and philosopher Whewell finds this "sagacity" quite 

 "out of the reach of method." The chemist G. N. Lewis writes: 



A detective with his murder mystery, a chemist seeking the structure 

 of a new compound, use little of the formal and logical modes of rea- 

 soning. Through a series of intuitions, surmises, fancies, they stum- 

 ble upon the right explanation, and have a knack of seizing it when it 

 once comes within reach. 



Einstein speaks for many distinguished physicists when he declares 

 that: 



. . . there is no logical way to the discovery of these elemental laws. 

 There is only the way of intuition, which is helped by a feeling for the 

 order lying behind the appearance. 



If the mathematician Poincare is right, something of the same sort 

 is true even within the domain of the formal disciplines : 



Logic has very little to do with discovery or invention. 



