232 SCIENTIFIC METHOD IN PHILOSOPHY 



which the effect varies as the previous readings increase 

 in number, and in fact Bergson himself tacitly assumes 

 such a law. We decide at last not to read the poem 

 again, because we know that this time the effect would 

 be boredom. We may not know all the niceties and 

 shades of the boredom we should feel, but we know 

 enough to guide our decision, and the prophecy of bore- 

 dom is none the less true for being more or less general. 

 Thus the kinds of cases upon which Bergson relies are 

 insufficient to show the impossibility of prediction in the 

 only sense in which prediction has practical or emotional 

 interest. We may therefore leave the consideration of 

 his arguments and address ourselves to the problem 

 directly. 



The law of causation, according to which later events 

 can theoretically be predicted by means of earlier events, 

 has often been held to be a priori^ a necessity of thought, 

 a category without which science would be impossible. 

 These claims seem to me excessive. In certain directions 

 the law has been verified empirically, and in other direc- 

 tions there is no positive evidence against it. But science 

 can use it where it has been found to be true, without 

 being forced into any assumption as to its truth in other 

 fields. We cannot, therefore, feel any a priori certainty 

 that causation must apply to human volitions. 



The question how far human volitions are subject to 

 causal laws is a purely empirical one. Empirically it 

 seems plain that the great majority of our volitions have 

 causes, but it cannot, on this account, be held necessarily 

 certain that all have causes. There are, however, precisely 

 the same kinds of reasons for regarding it as probable 

 that they all have causes as there are in the case of 

 physical events. 



We may suppose though this is doubtful that there 



