202 THE RIDDLE OF THE UNIVERSE. 



so forth. The childish naivety of this Platonic 

 morality is obvious ; on closer examination his views 

 are found to be absolutely incompatible with the 

 scientific truth which we owe to modern anatomy, 

 physiology, histology, and ontogeny ; we mention 

 them only because, in spite of their absurdity, they 

 have had a profound influence on thought and 

 culture. On the one hand, the mysticism of the 

 Neo-Platonists, which penetrated into Christianity, 

 attached itself to the psychology of Plato ; on the 

 other hand, it became subsequently one of the chief 

 supports of spiritualistic and idealistic philosophy. 

 The Platonic " idea " gave way in time to the notion 

 of psychic " substance "; this is just as incompre- 

 hensible and metaphysical, though it often assumed 

 a physical appearance. 



The conception of the soul as a " substance " is far 

 from clear in many psychologists ; sometimes it is 

 regarded as an " immaterial " entity of a peculiar 

 character in an abstract and idealistic sense, some- 

 times in a concrete and realistic sense, and sometimes 

 as a confused tertium quid between the two. If we 

 adhere to the monistic idea of substance, which we 

 develop in chap, xii., and which takes it to be the 

 simplest element of our whole world-system, we find 

 energy and matter inseparably associated in it. We 

 must, therefore, distinguish in the " substance of the 

 soul " the characteristic psychic energy which is all we 

 perceive (sensation, presentation, volition, etc.), and 

 the psychic matter, which is the indispensable basis of 

 its activity — that is, the living protoplasm. Thus, in 

 the higher animals the " matter " of the soul is a 

 part of the nervous system ; in the lower nerveless 

 animals and plants it is a part of their multicellular 



