INTRODUCTORY. 17 



in the abstract and the applied sciences of nature, and 

 which even make it possible to employ those methods 

 of measurement and calculation by which not only have 

 natural phenomena and processes been more clearly 

 described, but many have been discovered which other- 

 wise would have remained for ever unknown. We 

 there saw how these attempts, which I comprised under 



the title of the " psycho-physical view of nature," have 12. 



Psycho- 

 caused the elaboration of two theories which, like all physical 



view of 



fruitful theories, have been domiciled in scientific liter- nature - 

 ature by novel terms that have become widely current, 

 and are being largely used with a more or less clear 

 understanding of their meaning. The first of these is the 

 theory of " psycho-physical parallelism," which to put it 

 briefly maintains that every inner, psychical, pheno- 

 menon or process is accompanied by some outer physical 

 phenomenon or process in the human body, and that the 

 former can, to a great extent, be studied and understood 

 through the latter, which is its counterpart ; and this by 

 the same methods as those by which other physical phe- 

 nomena have been attacked. It is admitted that these 

 phenomena are extremely intricate, not to say puzzling 

 and mysterious ; but, it is said, not more so than those 

 exhibited in every other region of nature. A second 

 term which characterises and popularises this view is the 

 term " epi-phenomenon." l It has been introduced to 

 give expression to the conception that there really exist 

 only physical or bodily phenomena and processes, that 

 what we call the inner states only intermittently and 

 transiently accompany the physical processes which 



1 In German, Begleiterscheinung, a less illogical term. 

 VOL. III. B 



