TRUTH 



of man's soul from that of the nearest related mammals. 

 The curious predisposition to a priori knowledge is really 

 the effect of the inheritance of certain structures of the 

 brain, which have been formed in man's vertebrate 

 ancestors slowly and gradually, by adaptation to an 

 association of experiences, and therefore of a posteriori 

 knowledge. Even the absolutely certain truths of mathe- 

 matics and physics, which Kant described as synthetic 

 judgments a priori, were originally attained by the 

 phyletic development of the judgment, and may be 

 reduced to constantly repeated experiences and a priori 

 conclusions derived therefrom. The "necessity" which 

 Kant considered to be a special feature of these a priori 

 propositions would be found in all other judgments if we 

 were fully acquainted with the phenomena and their con- 

 ditions. 



Among the censures which the academic metaphysi- 

 cians, especially in Germany, have passed on my Riddle of 

 the Universe, the heaviest is perhaps the charge that I 

 know nothing whatever about the theory of knowledge. 

 The charge is correct to this extent, that I do not under- 

 stand the current dualistic theory of knowledge which is 

 based on Kant's metaphysics; I cannot understand how 

 their introspective psychological methods — disdaining 

 all physiological, histological, or phylogenetic founda- 

 tions — can satisfy the demands of "pure reason." My 

 monistic theory of knowledge is assuredly very different 

 from this. It is firmly and thoroughly based on the 

 splendid advances of modern physiology, histology, and 

 phylogeny — on the remarkable results of these empirical 

 sciences in the last forty years, which are entirely 

 ignored by the prevailing system of metaphysics. It is 

 on the ground of these experiences that I have adopted 

 the views on the nature of the human mind which are ex- 

 pounded in the second part of The Riddle of the Universe 

 (chapters vi.-xi.). The following are the chief points: 



II 



