ON THE NOTION OF CAUSE 237 



be established by the other sciences, and conversely must 

 not be such as some other science might conceivably con- 

 tradict. Prophecies as to the future of the universe, for 

 example, are not the business of philosophy ; whether 

 the universe is progressive, retrograde, or stationary, it 

 is not for the philosopher to say. 



In order to become a scientific philosopher, a certain 

 peculiar mental discipline is required. There must be 

 present, first of all, the desire to know philosophical 

 truth, and this desire must be sufficiently strong to 

 survive through years when there seems no hope of its 

 finding any satisfaction. The desire to know philo- 

 sophical truth is very rare in its purity, it is not often 

 found even among philosophers. It is obscured some- 

 times particularly after long periods of fruitless search 

 by the desire to think we know. Some plausible 

 opinion presents itself, and by turning our attention away 

 from the objections to it, or merely by not making great 

 efforts to find objections to it, we may obtain the comfort 

 of believing it, although, if we had resisted the wish for 

 comfort, we should have come to see that the opinion 

 was false. Again the desire for unadulterated truth is 

 often obscured, in professional philosophers, by love of 

 system : the one little fact which will not come inside 

 the philosopher's edifice has to be pushed and tortured 

 until it seems to consent. Yet the one little fact is more 

 likely to be important for the future than the system 

 with which it is inconsistent. Pythagoras invented a 

 system which fitted admirably with all the facts he knew, 

 except the incommensurability of the diagonal of a square 

 and the side ; this one little fact stood out, and remained 

 a fact even after Hippasos of Metapontion was drowned 

 for revealing it. To us, the discovery of this fact is the 

 chief claim of Pythagoras to immortality, while his 



