CLASSIFICATION AND THE PREDICABLES. 



79 



did mean something by this distinc- 

 tion, and something important ; but 

 which, being but indistinctly con- 

 ceived, was inadequately expressed 

 by the phraseology of essences, and 

 the various other modes of speech to 

 which they had recourse. 



§ 4. It is a fundamental principle 

 in logic, that the power of framing 

 classes is unlimited, as long as there 

 is any (even the smallest) difference 

 to found a distinction upon. Take 

 any attribute whatever, and if some 

 things have it, and others have not, 

 we may ground on the attribute a 

 division of all things into two classes ; 

 and we actually do so the moment 

 we create a name which connotes the 

 attribute. The number of possible 

 classes, therefore, is boundless ; and 

 there are as many actual classes (either 

 of real or of imaginary things) as there 

 are general names, positive and nega- 

 tive together. 



But if we contemplate any one of 

 the classes so formed, such as the class 

 animal or plant, or the class sulphur 

 or phosphorus, or the class white or 

 red, and consider in what particulars 

 the individuals included in the class 

 differ from those which do not come 

 within it, we find a very remarkable 

 diversity in this respect between some 

 classes and others. There are some 

 classes, the things contained in which 

 differ from other things only in certain 

 particulars which may be numbered, 

 while others differ in more than can 

 be numbered, more even than we need 

 ever expect to know. Some classes 

 have little or nothing in common to 

 characterise them by, except precisely 

 what is connoted by the name : white 

 things, for example, are not distin- 

 guished by any common properties 

 except whiteness ; or if they are, it is 

 only by such as are in some way de- 

 pendent on, or connected with, white- 

 ness. But a hundred generations 

 have not exhausted the common pro- 

 perties of animals or of plants, of 

 sulphur or of phosphorus ; nor do 

 we suppose them to be exhaustible, j 



but proceed to new observations and 

 experiments, in the full confidence of 

 discovering new properties which 

 were by no means implied in those we 

 previously knew. While, if any one 

 were to propose for investigation the 

 common properties of all things which 

 are of the same colour, the same 

 shape, or the same specific gravity, 

 the absurdity would be palpable. 

 We have no ground to believe that 

 any such common properties exist, 

 except such as may be shown to be 

 involved in the supposition itself, or 

 to be derivable from it by some law 

 of causation. It appears, therefore, 

 that the properties, on which we 

 ground our classes, sometimes exhaust 

 all that the class has in common, or 

 contain it all by some mode of impli- 

 cation ; but in other instances we 

 make a selection of a few properties 

 from among not only a greater num- 

 ber, but a number inexhaustible by 

 us, and to which, as we know no 

 bounds, they may, so far as we are 

 concerned, be regarded as infinite. 



There is no impropriety in saying 

 that, of these two classifications, the 

 one answers to a much more radical 

 distinction in the things themselves 

 than the other does. And if any one 

 even chooses to say that the one classi- 

 fication is made by nature, the other 

 by us for our convenience, he will be 

 right ; provided he means no more 

 than this : Where a certain apparent 

 difference between things (though per- 

 haps in itself of little moment) answers 

 to we know not what number of other 

 differences, pervading not only their 

 known properties, but properties yet 

 undiscovered, it is not optional but 

 imperative to recognise this difference 

 as the foundation of a specific dis- 

 tinction ; while, on the contrary, dif- 

 ferences that are merely finite and 

 determinate, like those designated by 

 the words white, black, or red, may 

 be disregarded if the purpose for 

 which the classification is made does 

 not require attention to those par- 

 ticular properties. The differences, 

 however, are made by nature, in both 



