294 ixVDUCTiox. 



in the former case it is only useful by suggesting a line of investigation 

 which may possibly terminate in obtaining real proof For this pixr- 

 pose, as is justly remarked by M. Comte (who of all philosophers 

 seems to me to have- approached the nearest to a sound view of this 

 important subject), it is indispensable that the cause suggested by the 

 hypothesis should be in its o\%ti nature susceptible of being proved by 

 other evidence. This seems to be the philosophical import of Newton's 

 maxim (so often cited with approbation by subsequent A\Triters), that 

 the cause assigned for any phenomenon must not only be such as if 

 admitted would explain the phenomenon, but must also be a vera causa. 

 What he meant by a vera causa Newton did not indeed very explicitly 

 define ; and I\Ir. AVhewell, who dissents from the propriety of any such 

 restriction upon the latitude of framing hypotheses, has had little diffi- 

 culty in showing* that his conception of it was neither precise nor con- 

 sistent with itself: accordingly his optical theory was a signal instance 

 of the violation of his owm rule. And Mr. AVhewell is clearly right in 

 denying it to be necessary that the cause assigned should be a cause 

 already known ; else how could we ever become acquainted with any 

 new cause? But what is true in the maxim is, that the cause, although 

 not kno-vvn previously, should be capable of being kno\vn thereafter ; 

 that its existence should be capable of being detected, and its con- 

 nexion with the effect ascribed to it, susceptible of being proved, by 

 independent e\-idence. The hypothesis, by suggesting obsei"\-ations 

 and experiments, puts us upon the road to that independent evidence 

 if it be really attainable ; and till it be attained, the hypothesis ought 

 not to count for more than a suspicion. 



§ 5. This function, however, of hypotheses, is one which must be 

 reckoned absolutely indispensable in science. A\'Tien Newton said, 

 " Hypotheses non fingo," he did not mean that he deprived himself of 

 the facilities of investigation afforded by assuming in the first instance 

 what he hoped ultimately to be able to prove. Without such assump- 

 tions, science could never have attained its present state : they are 

 necessary steps in the progress to something more certain ; ajid nearly 

 everything which is now theory was once hypothesis. Even in purely 

 experimental science, some inducement is necessary for tiying one 

 •experiment rather than another ; and although it is abstractedly possi- 

 ble that all the experiments which have been tried, might have been 

 produced by the mere desire to ascertain what would happen in certain 

 ■cii'cumstances, without any previous conjecture as to the result ; yet 

 in point of fact those unobvious, delicate, and often cumbrous and 

 tedious processes of experiment, which have thrown most light upon 

 the general constitution of nature, would hardly ever have been under- 

 taken by the persons or at the time they were, unless it had seemed 

 to depend upon 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 

 experimental into deductive truths could still less have been effected 

 without large temporary assistance from hypotheses. The process of 

 tracing regularity in any complicated and at first sight confused set of 

 appearances, is necessarily tentative : we begin by making any suppo 



* Philosophy of the Inductive Sciences, vol, ii., pp. 441-6. 



