PREFACE ix 



would be hard to estimate the amount of detri- 

 ment to clear thinking effected, directly and in- 

 directly, by the theory of ideas, on the one hand, 

 and by the unfortunate doctrine of the baseness of 

 matter, on the other. 



Ancient thought, so far as it is positive, fails on 

 account of its neglect to criticise its assumptions; \ 

 so far as it is negative, it fails, because it forgets 

 that proof of the inconsistencies of the terms in 

 which we symbolise things has nothing to do with 

 the cogency of the logic of facts. The negations 

 of Pyrrhonism are as shallow, as the assumptions 

 of Platonism are ^npty. Modern thought has by 

 no means escaped from " perversions of the same 

 order. But, thanks to the sharp discipline of 

 physical science, it is more and more freeing itself 

 from them. In face of the incessant verification 

 of deductive reasoning by experiment, Pyrrhonism 

 has become ridiculous; in face of the ignominious 

 fate which always befalls those who attempt to get 

 at the secrets of nature, or the rules of conduct, 

 by the high a priori road, Platonism and i* 

 modern progeny show themselves to be, at best, 

 splendid follies. 



The development of exact natural knowledge 

 in all its vast range, from physics to history and 

 criticism, is the consequence of the working out, 

 in this province, of the resolution to " take nothing 

 for truth without clear knowledge that it is such; " 

 to consider all beliefs open to criticism; to regard 



