VI PREFACE. 



tain data uncritically, and declines to challenge the ele- 

 ments between which its own ' laws ' obtain, and from 

 which its own deductions are carried on. Psychology, the 

 science of finite individual minds, assumes as its data (1) 

 thoughts and feelings, and (2) a physical ivorld in time and 

 space with which they coexist and which (3) they knotv. Of 

 course these data themselves are discussable ; but the dis- 

 cussion of them (as of other elements) is called meta- 

 physics and falls outside the province of this book. This 

 book, assuming that thoughts and feelings exist and are 

 vehicles of knowledge, thereupon contends that psychology 

 when she has ascertained the empirical correlation of the 

 various sorts of thought or feeling with definite conditions 

 of the brain, can go no farther — can go no farther, that is, 

 as a natural science. If she goes farther she becomes 

 metaphysical. All attempts to explain our phenomenally 

 given thoughts as products of deeper-lying entities 

 (whether the latter be named * Soul,' ' Transcendental 

 Ego,' * Ideas,' or ' Elementary Units of Consciousness ') are 

 metaphysical. This book consequently rejects both the 

 associationist and the spiritualist theories ; and in this 

 strictly positivistic point of view consists the only feature 

 of it for which I feel tempted to claim originality. Of 

 course this point of view is anything but ultimate. Men 

 must keep thinking ; and the data assumed by psychology, 

 just like tljose assumed by physics and the other natural 

 sciences, must some time be overhauled. The efi'ort to 

 overhaul them clearly and thoroughly is metaphysics ; 

 but metaphysics can only perform her task well when dis- 

 tinctly conscious of its great extent. Metaphysics fragmen- 

 tary, irresponsible, and half-awake, and unconscious that 

 she is metaphysical, spoils two good things when she in- 

 jects herself into a natural science. And it seems to me 

 that the theories both of a spiritual agent and of associated 

 ' ideas' are, as they figure in the psychology-books, just such 

 metaphysics as this. Even if their results be true, it 

 would be as w^ell to keep them, as thus presented, out of 

 psychology as it is to keep the results of idealism out of 

 physics. 



I have therefore treated our passing thoughts as inte- 



