122 THE SCIENCE OF LOGIC 



inventor will have free scope (197). Wrong hypotheses will be 

 usually conceived before right ones. Kepler is said to have 

 conceived and disproved nineteen successively, before arriving at 

 the laws of planetary motion. 1 It must not, however, be imagined 

 that hypotheses are useless unless they turn out to be true ; they 

 often admirably fulfil their function of directing investigation, and 

 do immense service to science, even though they be afterwards 

 disproved. Thus, in astronomy we have the famous example ot 

 the Ptolemaic or geocentric hypothesis, which gave place to the 

 Copernican or heliocentric hypothesis in the sixteenth century. 



The conception of an hypothesis which is likely to prove 

 useful, and helpful to the progress of science, is usually possible 

 only to the well-trained mind that is stocked with information 

 about the matter under investigation, and is accordingly quick to 

 detect and utilize analogies. To such a mind, even the most 

 commonplace facts may suggest invaluable lines of speculation 

 and experiment as the falling apple did for Newton, and the 

 dancing lid of the steaming kettle did for Watt. Whewell was 

 therefore right in emphasizing, as against Mill, the great import 

 ance of hypothesis, or as he called it, &quot;colligation of facts by 

 means of an exact and appropriate conception,&quot; in the whole 

 inductive process. 2 But there are various kinds of hypotheses; 

 and some are &quot; more far-reaching in their effects than others ; for 

 some are much more general, and apply to a much larger 

 number and variety of facts. . . . Scientific hypotheses consist 

 for the most part not in the mere coupling in the mind, as cause 

 and effect, of two insulated phenomena (if the epithet may be 

 allowed) : but in the weaving of a large number of phenomena 

 into a coherent system by means of principles that fit the facts &quot;. 3 

 This brings us to the consideration of some of the principal types 

 of scientific hypothesis. 



227. SCIENTIFIC VALUE OF VARIOUS KINDS OF HYPOTHESIS. 

 We have described an hypothesis as a provisional explanation 

 of certain observed facts. Now, we know a fact scientifically 

 when we know all its causes, and the mode of its connexion with, 

 or dependence on, these causes. If we take any phenomenon, or 

 group of phenomena, involving within it a multiplicity of elements, 

 changes, motions, activities for example, the motions of the 



1 C/. WELTON, op. cit., ii., pp. 66, 86. JOSEPH, op. cit., pp. 435-6. 

 a Cf. WELTON, op. cit., pp. 48 sqq. JOSEPH, op. cit., p. 434. 

 3 JOSEPH, ibid., pp. 432, 433. 



