THE NATURE OF THE PROBLEM. 19 



knowledge, sense-experience and rational thought, are 

 two distinct cerebral functions ; the one is elaborated 

 by the sense-organs and the inner sense-centres, the 

 other by the thought-centres, the great " centres of 

 association in the cortex of the brain," which lie 

 between the sense-centres. (Cf. cc. vii. and x.) True 

 knowledge is only acquired by combining the activity 

 of the two. Nevertheless, there are still many philo- 

 sophers who would construct the world out of their 

 own inner consciousness, and who reject our empirical 

 science precisely because they have no knowledge of 

 the real world. On the other hand, there are many 

 scientists who still contend that the sole object of 

 science is " the knowledge of facts, the objective inves- 

 tigation of isolated phenomena "; that " the age of 

 philosophy " is past, and science has taken its place. 1 

 This one-sided over-estimation of experience is as 

 dangerous an error as the converse exaggeration of 

 the value of speculation. Both channels of knowledge 

 are mutually indispensable. The greatest triumphs 

 of modern science — the cellular theory, the dynamic 

 theory of heat, the theory of evolution, and the law 

 of substance — are philosophic achievements ; they are 

 not, however, the fruit of pure speculation, but of an 

 antecedent experience of the widest and most searching 

 character. 



At the commencement of the nineteenth century 

 the great idealistic poet, Schiller, gave this counsel to 

 both groups of combatants, the philosophers and the 

 scientists : — 



" Does strife divide your efforts — no union bless your toil? 

 Will truth e'er be delivered if ye your forces rend ?" 



1 Rudolph Virchow, Die grilndung der Berliner Universitdt und der 

 ilbergang aus dem philosophischen in das natunvissenschaftliche zeit- 

 alter. (Berlin; 1893.) 



