322 



INDUCTION. 



vibratory motion, are not proved, but 

 are assumed, on no other ground than 

 the facility they are supposed to 

 afford of explaining the phenomena. 

 And this consideration leads to the 

 important question of the proper use 

 of scientific hypotheses ; the connec- 

 tion of which with the subject of the 

 explanation of the phenomena of 

 nature, and of the necessary limits 

 to that explanation, needs not be 

 pointed out. 



§ 4. An hypothesis is any supposi- 

 tion which we make (either without 

 actual evidence, or on evidence avow- 

 edly insufficient) in order to endeavour 

 to deduce from it conclusions in ac- 

 cordance with facts which are known 

 to be real ; under the idea that if the 

 conclusions to which the hypothesis 

 leads are known truths, the hypo- 

 thesis itself either must be, or at least 

 is likely to be, true. If the hypo- 

 thesis relates to the cause or mode pf 

 production of a phenomenon, it will 

 serve, if admitted, to explain such 

 facts as are found capable of being 

 deduced from it. And this explana- 

 tion is the purpose of many, if not 

 most, hypotheses. Since explaining, 

 in the scientific sense, means resolving 

 an uniformity which is not a law of 

 causation into the laws of causation 

 from which it results, or a complex 

 law of causation into simpler and 

 more general ones from which it is 

 capable of being deductively inferred; 

 if there do not exist any known laws 

 which fulfil this requirement, we may 

 feign or imagine some which would 

 fulfil it ; and this is making an hjrpo- 

 thesis. 



An hjrpothesis being a mere sup- 

 position, there are no other limits to 

 hypotheses than those of the human 

 imagination ; we may, if we please, 

 imagine, by way of accounting for an 

 effect, some cause of a kind utterly 

 unknown, and acting according to a 

 law altogether fictitious. But as hypo- 

 theses of this sort would not have any 

 of the plausibility belonging to those 

 >vhich all^ themselves by analogy 



with known laws of nature, and 

 besides would not supply the want 

 which arbitrary hypotheses are gene- 

 rally invented to satisfy, by enabling 

 the imagination to represent to itself 

 an obscure phenomenon in a familiar 

 light, there is probably no hypothesis 

 in the history of science in which both 

 the agent itself and the law of its 

 operation were fictitious. Either the 

 phenomenon assigned as the cause is 

 real, but the law according to which 

 it acts merely supposed, or the cause 

 is fictitious, but is supposed to pro- 

 duce its effects according to laws 

 similar to those of some known class 

 of phenomena. An instance of the 

 first kind is afforded by the different 

 suppositions made respecting the law 

 of the planetary central force an- 

 terior to the discovery of the true law, 

 that the force varies as the inverse 

 square of the distance ; which also 

 suggested itself to Newton, in the first 

 instance, as an hypothesis, and was 

 verified by proving that it led de- 

 ductively to Kepler's laws. Hypo- 

 theses of the second kind are such as 

 the vortices of Descartes, which were 

 fictitious, but were supposed to obey 

 the known laws of rotatory motion ; 

 or the two rival hypotheses respecting 

 the nature of light, the one ascribing 

 the phenomena to a fluid emitted from 

 all luminous bodies, the other (now 

 generally received) attributing them 

 to vibratory motions among the par- 

 ticles of an ether pervading all space. 

 Of the existence of either fluid there 

 is no evidence, save the explanation 

 they are calculated to afford of some 

 of the phenomena ; but they are sup- 

 posed to produce their effects accord- 

 ing to known laws ; the ordinary laws 

 of continued locomotion in the one 

 case, and in the other, those of the 

 propagation of undulatory movements 

 among the particles of an elastic fluid. 

 According to the foregoing remarks, 

 hypotheses are invented to enable the 

 Deductive Method to be earlier ap- 

 plied to phenomena. But* in order 

 to discover the cause of any pheno» 

 * y|d« lupra, book |ii. oh. xi, 



