ILLUSTRATIONS OF THE LOGIC OF SCIENCE. 481 



Induction is, plainly, a much stronger kind of inference than hy- 

 pothesis ; and this is the first reason for distinguishing between them. 

 Hypotheses are sometimes regarded as provisional resorts, which in the 

 progress of science are to be replaced by inductions. But this is a false 

 view of the subject. Hypothetic reasoning infers very frequently a 

 fact not capable of direct observation. It is an hypothesis that Napo- 

 leon Bonaparte once existed. How is that hypothesis ever to be re- 

 placed by an induction ? It may be said that from the premise that 

 such facts as we have observed are as they would be if Napoleon exist- 

 ed, we are to infer by induction that all facts that are hereafter to be ob- 

 served will be of the same character. There is no doubt that every hy- 

 pothetic inference may be distorted into the appearance of an induction 

 in this way. But the essence of an induction is that it infers from one 

 set of facts another set of similar facts, whereas hypothesis infers from 

 facts of one kind to facts of another. Now, the facts which serve as 

 grounds for our belief in the historic reality of Napoleon are not by any 

 means necessarily the only kind of facts which are explained by his ex- 

 istence. It may be that, at the time of his career, events were being re- 

 corded in some way not now dreamed of, that some ingenious creature 

 on a neighboring planet was photographing the earth, and that these 

 pictures on a sufficiently large scale may some time come into our poses- 

 sion, or that some mirror upon a distant star will, when the light 

 reaches it, reflect the whole story back to earth. Never mind how im- 

 probable these suppositions are ; everything which happens is infinitely 

 improbable. I am not saying that these things are likely to occur, but 

 that some effect of Napoleon's existence which now seems impossible is 

 certain nevertheless to be brought about. The hypothesis asserts that 

 such facts, when they do occur, will be of a nature to confirm, and not 

 to refute, the existence of the man. We have, in the impossibility of 

 inductively inferring hypothetical conclusions, a second reason for dis- 

 tinguishing between the two kinds of inference. 



A third merit of the distinction is, that it is associated with an im- 

 portant psychological or rather physiological difference in the mode of 

 apprehending facts. Induction infers a rule. Now, the belief of a rule 

 is a habit. That a habit is a rule active in us, is evident. That every 

 belief is of the nature of a habit, in so far as it is of a general charac- 

 ter, has been shown in the earlier papers of this series. Induction, 

 therefore, is the logical formula which expresses the physiological pro- 

 cess of formation of a habit. Hypothesis substitutes, for a complicated 

 tangle of predicates attached to one subject, a single conception. Now, 

 there is a peculiar sensation belonging to the act of thinking that each 

 of these predicates inheres in the subject. In hypothetic inference 

 this complicated feeling so produced is replaced by a single feeling of 

 greater intensity, that belonging to the act of thinking the hypothetic 

 conclusion. Now, when our nervous system is excited in a complicated 

 way, there being a relation between the elements of the excitation, the 



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