THE USE OF HYPOTHESIS. 139 



about 700 billions of vibrations in each second, are state- 

 ments of an inconceivable and absurd character in one 

 sense ; but they are so far from being opposed to fact that 

 we cannot on any other suppositions account for the phe- 

 nomena observed. But if an hypothesis involve self-con- 

 tradiction, or is inconsistent with known laws of nature, it 

 is so far self-condemned. We cannot even apply processes 

 of deductive reasoning to a self-contradictory notion ; and 

 being entirely opposed to the most general and certain 

 laws known to us, the primary laws of thought, it thereby 

 conspicuously fails to agree with facts. Since nature, 

 again, is never self-contradictory, we cannot at the same 

 time accept two theories which lead to contradictory 

 results. If the one agrees with nature, the other cannot. 

 Hence if there be a law which we believe with high pro- 

 bability to be verified in observation, we must not frame 

 an hypothesis in conflict with it, otherwise the hypothesis 

 will necessarily be in disagreement with observation. 

 Since no law or hypothesis is proved, indeed, with ab- 

 solute certainty, there is always a chance, however slight, 

 that the new hypothesis may displace the old one ; but 

 the greater the probability which we assign to that old 

 hypothesis, the greater must be the evidence required in 

 favour of the new and conflicting one. A decisive ex- 

 perimentum crucis to negative the one, and establish the 

 other, will probably be requisite to allay the strife. 



I am inclined to assert, then, that there is but one test 

 of a good hypothesis, namely, its conformity with observed 

 facts; but this condition may be said to involve, at the 

 same time, three minor conditions, nearly equivalent to 

 those suggested by Hobbes and Boyle, namely : 



1 i ) That it allow of the application of deductive reason- 

 ing and the inference of consequences. 



(2) That it do not conflict with any laws of nature, or 

 of mind, which we hold as true. 



