INTRODUCTION. XXIX 



addition to their writings on the philosophy or the logic 

 of the sciences, have dealt expressly, and from the scien- 

 tific point of view, with ethical and social questions. It 

 is true, indeed, that both physical and vital phenomena 

 are manifested in the human subject, that man is both 

 a machine and an organism in which the law of the 

 transmutation of energy is fulfilled ; true, therefore, that 

 he is so far a proper subject for physical and biological 

 investigation ; still, neither the most important nor the 

 most interesting problems presented by man relate to 

 the mechanism, however express and admirable, of his 

 physical structure, nor to the transmutations of physical 

 into vital and mental energy which really has place 

 within the human machine. Nor do they relate to those 

 other facts of organic functions and their various rela- 

 tions, with which the science of physiology deals. The 

 most important problems presented by man from the 

 point of view of science are psychological, moral, and 

 social, and our scientific authorities may be credited 

 with having taken into consideration such physical and 

 physiological conclusions as have special and important 

 bearing on these questions. 



3. Thus far on the subject of authorities. But it 

 may be said, If your exposition be unexceptionable, and 

 your finding of faith and doctrine accurately gathered 

 from the first and surest sources as respects each par- 

 ticular article, is it not a little presumptuous to affect 

 thereafter to criticise such acknowledged authorities ? 



I think not, and for the following reasons : In the 

 first place, we must distinguish between scientific faith 

 and scientific fact, between a fully verified law and a 

 supposed inference hazarded from it without being con- 

 tained under it, between a well-established theory and 



