326 



INDUCTION, 



only be such as, if admitted, would 

 explain the phenomenon, but must 

 also be a vera cau^a. What he meant 

 by a vera causa Newton did not in- 

 deed very explicitly define ; and Dr. 

 Whewell, who dissents from the pro- 

 priety of any such restriction upon 

 the latitude of framing hj'potheses, 

 has had little difficulty in showing * 

 that his conception of it was neither 

 precise nor consistent with itself : ac- 

 cordingly his optical theory was a 

 signal instance of the violation of his 

 own rule. It is certainly not neces- 

 sary that the cause assigned should 

 be a cause already known ; otherwise 

 we should sacrifice our best oppor- 

 tunities of becoming acquainted with 

 new causes. But what is true in the 

 maxim is, that the cause, though not 

 known previously, should be capable 

 of being known thereafter ; that its 

 existence should be capable of being 

 detected, and its connection with the 

 eflfect ascribed to it should be suscep- 

 tible of being proved, by independent 

 evidence. The hypothesis, by sug- 

 gesting observations and experiments, 

 puts us on the road to that inde- 

 pendent evidence if it be really at- 

 tainable ; and till it be attained, the 

 hypothesis ought only to count for a 

 more or less plausible conjecture. 



§ 5. This function, however, of 

 hypotheses, is one which must be 

 reckoned absolutely indispensable in 

 science. When Newton said, " Hypo- 

 theses non fingo," he did not mean 

 that he deprived himself of the facili- 

 ties of investigation afforded by as- 

 suming in the first instance what he 

 hoped ultimately to be able to prove. 

 Without such assumptions, science 

 could never have attained its present 

 state : they are necessary steps in the 

 progress to something more certain ; 

 and nearly everything which is now 

 theory was once hypothesis. Even 

 in purely experimental science, some 

 inducement is necessary for trying 

 one experiment rather than another ; 



* Philoiojphy of Discover}/, pp, 185 et seq. . 



and though it is abstractly possible 

 that all the experiments which have 

 been tried might have been produced 

 by the mere desire to ascertain what 

 would happen in certain circumstances, 

 without any previous conjecture as to 

 the result ; yet, in point of fact, those 

 unobvious, delicate, and often cum- 

 brous and tedious processes of ex- 

 periment, which have thrown most 

 light upon the general constitution of 

 nature, would hardly ever have been 

 undertaken by the persons or at the 

 time they were, unless it had seemed 

 to depend on them whether some 

 general doctrine or theory which had 

 been suggested, but not yet proved, 

 should be admitted or not. If this 

 be true even of merely experimental 

 inquiry, the conversion of experi- 

 mental into deductive truths could 

 still less have been effected without 

 large temporary assistance from hypo- 

 theses. The process of tracing regu- 

 larity in any complicated, and at first 

 sight confused set of appearances, is 

 necessarily tentative : we begin by 

 making any supposition, even a false 

 one, to see what consequences will 

 follow from it ; and by observing how 

 these differ from the real phenomena, 

 we learn what corrections to make 

 in our assumption. The simplest 

 supposition which accords with the 

 more obvious facts is the best to 

 begin with, because its consequences 

 are the most easily traced. This 

 rude hypothesis is then rudely cor- 

 rected, and the operation repeated ; 

 and the comparison of the conse- 

 quences deducible from the corrected 

 hypothesis with the observed facts 

 suggests still further correction, until 

 the deductive results are at last made 

 to tally with the phenomena. " Some 

 fact is as yet little understood, or 

 some law is unknown ; we frame on 

 the subject an hypothesis as accordant 

 as possible with the whole of the data 

 already possessed ; and the science, 

 being thus enabled to move forward 

 freely, always ends by leading to new 

 consequences capable of observation, 

 which either confirm or refute, un- 



