34 MENTAL EVOLUTION IN MAN. 



that, whether or not we choose to denominate by the word 

 abstraction the faculty of compounding simple ideas without 

 the faculty of naming the compounds, at the place where this 

 additional faculty of naming supervenes, so immense an 

 accession to the previous faculty is furnished, that any 

 system of psychological nomenclature must be highly 

 imperfect if it be destitute of terms whereby to recognize the 

 difference. For even if it were conceded by psychologists of 

 the opposite school that the essence of abstraction consists 

 in the compounding of simple ideas, and not at all in the 

 subsequent process of naming the compounds ; still the effect 

 of this subsequent process — or additional faculty — is so pro- 

 digious, that the higher degrees of abstraction which by it 

 are rendered possible, certainly require to be marked off, or to 

 be distinguished from, the lower degrees. Without, therefore, 

 in any way prejudicing the question as to whether we have 

 here a difference of degree or a difference of kind, I will 

 submit a classification of ideas which, while not open to 

 objection from either side of this question, will greatly help 

 us in our subsequent treatment of the question itself. 



The word " Idea " I will use in the sense defined in my 

 previous work — namely, as a generic term to signify indiffer- 

 ently any product of imagination, from the mere memory of 

 a sensuous impression up to the result of the most abstruse 

 generalization.* 



By " Simple Idea," " Particular Idea," or " Concrete Idea," 

 I understand the mere memory of a particular sensuous 

 perception 



By " Compound Idea," " Complex Idea," or " Mixed Idea," 

 I understand the combination of simple, particular, or concrete 

 ideas into that kind of composite idea which is possible with- 

 out the aid of language. 



Lastly, by " General Idea," " Abstract Idea," " Concept," 

 or *' Notion," I understand that kind of composite idea which 

 is rendered possible only by the aid of language, or by the 

 process of naming abstractions as abstractions. 



* Mental Evolution in Animals^ p. II 8. 



