318 MENTAL EVOLUTION IN ANIMALS. 



CHAPTEE XIX. 



Eeason. 



I shall begin this chapter by quoting from " Animal Intel- 

 ligence " my definition of the word " Eeason," in order that 

 my use of the word may be clearly understood. 



" Eeason is the faculty which is concerned in the inten- 

 tional adaptation of means to ends. It therefore implies the 

 conscious knowledge of the relation between means employed 

 and ends attained, and may be exercised in adaptation to 

 circumstances novel alike to the experience of the individual 

 and to that of the species." In other words, " it implies the 

 power of perceiving analogies or ratios, and is in this sense 

 equivalent to the term 'ratiocination,' or the faculty of 

 deducing inferences from a perceived equivalency of relations. 

 This latter is the only use of the word that is strictly legiti- 

 mate, and it is thus that I shall use it throughout the present 

 treatise. This faculty, however, of balancing relations, draw- 

 ing inferences, and so of forecasting probabilities, admits of 

 numberless degrees." 



The object of the present chapter will be that of tracing 

 the probable genesis of this faculty, and, in order to give 

 clearness to the discussion, I desire it to be remembered that 

 I reserve the terms Eeason and Eatiocination to designate 

 the faculty above defined. I shall use the term Inference to 

 designate the less highly developed mental antecedents out 

 of which, as I shall show, I conceive Eeason to have been 

 evolved. No doubt every act of reason is also an act of in- 

 ference, but we shall find that it is absolutely necessary to 

 have some word to signify indifferently the lowest and the 

 highest stages of that whole class of mental processes which 

 culminates in symbolic calculation. The word Inference is 



