INTRODUCTION. 15 



tion, and the rest, as implying mental faculties the same 

 in kind as those which in ourselves we call rational. 



Now it is notorious that no distinct line can be drawn 

 between instinct and reason. Whether we look to the 

 growing child or to the ascending scale of animal life, we 

 find that instinct shades into reason by imperceptible 

 degrees, or, as Pope expresses it, that these principles are 

 * for ever separate, yet for ever near.' Nor is this other 

 than the principles of evolution would lead us to expect, 

 as I shall afterwards have abundant occasion to show. 

 Here, however, we are only concerned with drawing what 

 distinction we can between instinct and reason as these 

 faculties are actually presented to our observation. And 

 this in a general way it is not difficult to do. 



We have seen that instinct involves 'mental opera- 

 tions,' and that by this feature it is distinguished from re- 

 flex action ; we have now to consider the features by which 

 it is distinguished from reason. These are accurately, 

 though not completely, conveyed by Sir Benjamin Brodie, 

 who defines instinct as ' a principle by which animals 

 are induced, independently of experience and reason- 

 ing, to the performances of certain voluntary acts, which 

 are necessary to their preservation as individuals, or 

 to the continuance of the species, or in some other 

 way convenient to them.' 1 This definition, as I have 

 said, is accurate as far as it goes, but it does not state 

 with sufficient generality and terseness that all instinctive 

 action is adaptive-; nor does it clearly bring out the dis- 

 tinction between instinct and reason which is thus we,ll 

 conveyed by the definition of Hartmann, who says in his 

 ' Philosophy of the Unconscious,' that ' instinct is action 

 taken in pursuance of an end, but without conscious per- 

 ception of what the end is.' This definition, however, is 

 likewise defective in that it omits another of the im- 

 portant differentiae of instinct namely, the uniformity of 

 instinctive action as performed by different individuals of 

 the same species. Including this feature, therefore, we 

 may more accurately and completely define instinct as 

 mental action (whether in animals or human beings), 

 1 Psychological Rcsearclies, p. 187. 



