12 INTRODUCTION. 



course, of enquiring into the causes which have determined it. 

 So far as observation is available to guide us in this enquiry, 

 I shall resort to no other assistance. Where, however, from 

 the nature of the case, observation fails us, I shall proceed to 

 inference. But though I shall use this method as sparingly 

 as possible, I am aware that criticism will often find valid 

 ground to object — ' It is all very well to map out the sup- 

 posed genesis of the various mental faculties in this way, but 

 we require some definite experimental or historical proof that 

 the genesis in question actually did take place in the order 

 and manner that you infer.' 



Now, in answer to this objection, I have only to say that 

 no one can have a more lively appreciation than myself of 

 the supreme importance of experimental or historical veri- 

 fication, in all cases where the possibility of such verification 

 is attainable. But in cases where such verification is not 

 attainable, what are we to do ? We may clearly do either of 

 two things. We may either neglect to investigate the sub- 

 ject at all, or we may Jo our best to investigate it by employ- 

 ing the only means of investigation which are at our disposal. 

 Of these two courses there can be no doubt which is the one 

 that the scientific spirit prompts. The true scientific spirit 

 desires to examine everything, and if in any case it is refused 

 the best class of instruments wherewith to conduct the 

 examination, it will adopt the next best that are available. 

 In such cases science clearly cannot be forwarded by neglect- 

 ing to use these instruments, while her cause may be greatly 

 advanced by using them with care. This is proved by the 

 fact that, in the science of psychology, nearly all the con- 

 siderable advances which have been made, have been made, 

 not by experiment, but by observing mental phenomena and 

 reasoning from these phenomena deductively. In such cases, 

 therefore, the true scientific spirit prompts us, not to throw 

 away deductive reasoning where it is so frequently the only 



