CHAPTER XXIII. 



THE USE OF HYPOTHESIS. 



IF the views of induction upheld in this work be 

 correct, all inductive investigation consists in a marriage 

 of hypothesis and experiment. When facts are already 

 in our possession, we frame an hypothesis to explain their 

 mutual relations, and by the success or non-success of this 

 explanation is the value of the hypothesis to be entirely 

 judged. In the framing and deductive treatment of such 

 hypotheses, we must avail ourselves of the whole body 

 of scientific truth already accumulated, and when once 

 we have obtained a probable hypothesis, we must not 

 rest until we have verified it by comparison with new 

 facts. By deductive reasoning and calculation, we must 

 endeavour to anticipate such new phenomena, especially 

 those of a singular and exceptional nature, as would 

 necessaiily happen if the hypothesis be true. Out of the 

 infinite number of observations and experiments which are 

 possible at every moment, theory must lead us to select 

 those few critical ones which are suitable for confirming 

 or negativing our anticipations. 



This work of inductive investigation cannot be guided 

 by any system of precise and infallible rules, like those of 

 deductive reasoning. There is, in fact, nothing to which 

 we can apply rules of method, because the laws of nature 

 to be treated must be in our possession before we can 

 treat them. If, indeed, there were any single rule of 



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