Psychophysical Parallelism in Evolution 15 



either series is sufficient to carry us over the critical point ; 

 if we have not, then the break in one series is sufficient 

 evidence of a corresponding break in the other also. 

 The principle of parallelism assumed, we claim once for 

 all the right to neglect the relation of the tivo terms, mental 

 and pJiysical, in all circumstances whatsoever. 1 



On this way of conceiving the scientific inquiry, we may 

 proceed unhampered by the problems which trouble the 

 philosopher. We do not have, for example, to adopt 

 Professor Lloyd Morgan's theory of 'metakinesis,' postu- 

 lating something quasi-mental to fill out the breaks in 

 the psychological series, at points at which we have no sign 

 of the presence of consciousness. Nor do we have to 

 embrace the idealistic theory of knowledge of his critic, 

 Professor Karl Pearson, to do away with a troublesome 

 brain substance, which at times becomes uncomfortably 

 prominent. The formulations of ' shorthand,' to use Pear- 

 son's phrase, may be made for both series together. 

 This is required for such a problem as that of evolution. 

 We do not have one series of genetic forms, the mental, 

 evolving under shorthand formulas of its own ; and 

 another series, the organic, doing the same thing under 

 different formulas. On the contrary, the two sets of facts 

 really go together in the one set of formulas. This is what 

 I am arguing for. We often find it necessary to use the 

 mental facts as antecedents of the physical facts, often 

 the physical as antecedent of the mental, and again, often 

 the psychophysical as antecedent of either or both. This 

 possibility is presented with more detail on a later page 

 (Chap. IX. 3). 



The twofold application of parallelism, considered as an 



1 Cf. the further remarks on the construction of heredity below, Chap. XVI. 



