HYPOTHESIS 121 



the earth we may suppose or imagine a cannon-ball travelling 

 at a velocity of five hundred yards per second and reaching the 

 moon after eight days : that image helps us to bring home to our 

 selves a distance so great that a mere statement of the number 

 of miles in it can hardly be pictured by us. But such a supposi 

 tion is not what we understand by a scientific hypothesis: it 

 belongs to the sphere of imagination exclusively, while a scientific 

 hypothesis is ^judgment bearing on our knowledge of reality. The 

 image of the cannon-ball gives us a clearer apprehension of some 

 thing we already knew ; an hypothesis aims at teaching us some 

 thing we did not know before. 1 Here is a simple example of a 

 scientific hypothesis : The juice of the grape ferments : the origin 

 and nature of fermentation were at one time unknown : Pasteur 

 conjectured that it was due to germs that swarm on the grapes, 

 leaves, and stems, of the vine-tree. That was a scientific hy 

 pothesis. 



An hypothesis , therefore, is an attempt at explanation : a pro 

 visional supposition made in order to explain scientifically some fact 

 or phenomenon. 



The construction of hypotheses is not confined to the induc 

 tive sciences. The process described in connexion with deductive 

 reasoning, by Aristotle and his mediaeval commentators, as &quot;tn- 

 ventio medii&quot; &quot; discovery of a middle term,&quot; i.e. of true and 

 proper premisses to prove a conclusion, is really identical with 

 what we nowadays call the conception or construction of an 

 hypothesis. But it is in the positive or inductive sciences that 

 hypothesis plays an all-important role. And in these sciences 

 we understand by it the conception or supposition of some cause 

 or law capable of explaining certain observed facts. Without 

 hypothesis we can make no progress in scientific investigation. 

 We cannot find the causes of phenomena without first suspecting 

 their existence and whereabouts. Our experiments will lead 

 nowhere unless made with the object of verifying some supposition. 

 To direct our investigations along certain lines towards the dis 

 covery of laws : such, in a word, is the function of hypothesis. 



All hypotheses should have their origin in the observed facts 

 which we are attempting to explain (233, 234). But the actual 

 conception of hypotheses is amenable to no logical rules. It is just 

 here that the sagacity, genius, and originality, of the scientist and 



1 Cf. MERCIER, Logique, p. 334. 



