SKEPTICISM AND IDOLATRY 201 



experiment confirms his conclusions, will he think that 

 he has demonstrated, for instance, the real existence of 

 atoms? " 



' These neutral hypotheses are never dangerous, if 

 only their character is not misunderstood. They may 

 be useful, either as devices for computation, or to aid 

 our understanding by concrete images, to fix our ideas 

 as the saying is. There is, then, no occasion to ex- 

 clude them. 



" The hypotheses of the third class are the real gen- 

 eralizations. They are the ones that experiment must 

 confirm or invalidate. Whether verified or condemned, 

 they will always be fruitful. But for the reasons that 

 I have set forth, they will only be fruitful if they are 

 not too numerous." 



It would seem to almost anyone that the first and 

 third classes are so different from the second class, 

 that it is advisable to call them laws, and limit the 

 term hypothesis to the speculative second class. The 

 class of neutral hypotheses is evidently the melting-pot 

 for the bewildering ethers, atoms, subtile fluids which 

 abound in the physical sciences, and which have their 

 analogues in all the others. Poincare teaches us that 

 we shall never acquire any definite knowledge from 

 them, and then he makes the amazing statement that 

 there is no need to exclude them if they are not mul- 

 tiplied, if they are made one after the other, and if 

 their character is not misunderstood. Anyone in the 



