138 THE PRINCIPLES OF SCIENCE. 



which are, as far as can be foreseen at the moment, most 

 probable. Each experiment, therefore, which he performs 

 is that most likely to throw light upon his subject, and 

 even if it frustrate his first views, it probably tends to 

 put him in possession of the correct clue. 



Requisites of a Good Hypothesis. 



There will be no difficulty in pointing out to what 

 conditions, or rather to what condition an hypothesis must 

 conform in order to be accepted as valid and probable. 

 That condition, as I conceive, is the single one of enabling 

 us to infer the existence of phenomena which occur in our 

 experience. Agreement with fact is the one sole and 

 sufficient test of a true hypothesis. 



Hobbes, indeed, has named two conditions which he 

 considers requisite in an hypothesis, namely, (i) That it 

 should be conceivable and not absurd ; (2) That it should 

 allow of phenomena being necessarily inferred. Boyle, in 

 noticing Hobbes' views, proposed to add a third condition, 

 to the effect that the hypothesis should not be inconsistent 

 with any other truth or phenomenon of nature 6 . Of 

 these three conditions, I am inclined to think that the 

 first cannot be accepted, unless by inconceivable and absurd 

 we mean self-contradictory or inconsistent with the laws 

 of thought and nature. I shall have to point out that 

 some of the most sure and satisfactory theories involve 

 suppositions which are wholly inconceivable in a certain 

 sense of the word, because the mind cannot sufficiently 

 extend its ideas to frame a notion of the actions supposed 

 to exist. That the force of gravity should act instan- 

 taneously between the most distant parts of the planetary 

 system, or that a ray of violet light should consist of 



6 Boyle's ' Physical Examen,' p. 84. 



