In my opinion so much has to be said in favour of both of these views that I am not going to pronounce against either. What I have hitherto been endeavouring to do is to reveal clearly that the question whether or not there is any difference between the brute and the man in respect of abstraction, is nothing more than a question of terminology. The real question will arise only when we come to treat of the faculty of language: the question before us now is merely a question of psychological classification, or of the nomenclature of ideas. Now, it appears to me that this question admits of being definitely settled, and a great deal of needless misunderstanding removed, by a slight re-adjustment and a closer definition of terms. For it must be on all hands admitted 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 prodigious, 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 indifferently any product of imagination, from the mere memory of a sensuous impression up to the result of the most abstruse generalization.[23] 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 without 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.