ON HUMAN UNDERSTANDING, 



397 



it as a character to a variety of other objects : and hence particular ideas 

 become general or universal. 



Other complex ideas are produced by comparison. Thus, if the mind 

 take one idea, as that of a foot, as a determinate measure, and place it by 

 the side of another idea, as the idea of a table, the result will be a forma- 

 tion of the complex idea of length, breadth, and thickness. Or if we 

 vary the primary ideas, we may obtain as a result, the secondary ideas of 

 coarseness and fineness. 



And hence complex ideas must be almost infinitely more numerous than 

 ^mple ideas, which are their elements or materials, as words must be 

 always far more numerous than letters. I have instanced only a few of 

 their principal kinds ; but even each of these kinds is applicable to a 

 variety of subjects, of which Mr. Locke mentions the three following : 



I. Ideas of Substances ; or such as we have uniformly found connected 

 in the same thing, and without which, therefore, such thing cannot be 

 contemplated. To this head belong the complex ideas of a man, a 

 horse, a river, a mountain. 



II. Ideas of Modes ; or such as may be considered as representative of 

 the mere affections, or properties of substance ; of which the idea of num- 

 ber may once more be offered as an example : the ideas of expansion or 

 extension and duration belong to the same stock ; and in like manner those 

 of power, time, space, and infinity, which are all modes, properties, or af- 

 fections of substance ; or secondary ideas derived from or excited by the 

 primary idea of substance of some kind or other. 



III. Ideas of Relations ; which are by far the most extensive, if not 

 the most important, branch of subjects from which our complex ideas are 

 derived ; for there is nothing whatever, whether simple idea"; substance, 

 mode, relation, or even the name of any of them, which is not capable of 

 an almost infinite number of bearings in reference or relation to other things. 

 It is from this source, therefore, that we derive a very large proportion of 

 our thoughts and words. As examples under it, I may mention all those 

 ideas that relate to, or are even imported by the terms father, brother, son, 

 master, magistrate, younger, older, cause and effect, right and wrong, and 

 consequently all moral relations. 



It must hence appear obvious that many of our ideas have a natural 

 correspondence, congruity, and connexion with each other. And as 

 many, perhaps, on the contrary, a natural repugnancy, incongruity, 

 and disconnexion. Thus if I were to speak of a cold fire, I should put 

 together ideas that are naturally disconnected and incongruous, and should 

 consequently make an absurd proposition, or, to adopt common language, 

 talk nonsense. I should be guilty of the same blunder if I were to speak 

 of a square billiard ball, or a soft reposing rock. But a warm fire, on the 

 contrary, a white, or even a black billiard ball, and a hard, rugged rock, 

 are congruous ideas, and consequently consistent with good sense. Now 

 it is the direct office of that discursive faculty of the mind which we call 

 reason, to trace out these natural coincidences or disjunctions, and to 

 connect or separate them by proper relations. For it is a just perception 

 of the natural connexion and congruity, or of the natural repugnancy and 

 incongruity of our ideas, that constitutes all real knowledge. The wise 

 man is he who has industriously laid in and carefully assorted an extensive 

 stock of ideas ; as the stupid or ignorant man is he who, from natural hebe- 

 tude, or having had but few opportunities, has collected and arranged but 

 a small number. The man who discovers the natural relations of his ideas 



