84 NAMES AND PROPOSITIONS. 



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 implication; but in 

 other instances we make a selection of a few properties from among 

 not only a greater number, but a number inexhaustible h^ 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 them- 

 selves, than the other does. And if any one even chooses to say that 

 the one classification is made by nature, the other by us for our conve- 

 nience, he will be right ; pro\"ided he means no more than this — that 

 where a certain apparent difference between things (although perhaps 

 in itself of little moment) answers to we know not what number of 

 other differences, pei'\'ading not only their known properties but prop- 

 erties yet undiscovered, it is not optional but imperative to recognize 

 this difference as the foundation of a specific distinction : while, on the 

 contrary, differences 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 atten- 

 tion to those particular properties. The differences, however, are made 

 by nature, in both cases ; while the recognition of those differences as 

 grounds of classification and of naming, is, equally in both cases, the act 

 of man : only in the one case, the ends of language and of classification 

 would be subverted if no notice were taken of the difference, while in 

 the other case, the necessity of taking notice of it depends upon the 

 importance or unimportance of the particular qualities in which the 

 difference happens to consist. 



Now, these classes, distinguished by unknown multitudes of prop- 

 erties, and not solely by a few determinate ones, are the only classes 

 which, by the Aristotelian logicians, were considered as genera or 

 species. Differences which extended to a certain property or proper- 

 ties, and there tenninated, they considered as differences only in the 

 accidents of things ; but where any class differed fi-om other things by 

 an infinite series of differences, known and unknown, they considered 

 the distinction as one of kind, and spoke of it as being an essential 

 difference, which is also one of the usual meanings of that vague ex- 

 pression at the present day. 



Conceiving the schoolmen to have been justified in drawing a broad 

 line of separation between these two kinds of classes and of class-dis- 

 tinctions, I shall not only retain the di\'ision itself, but continue to 

 express it in their language. According to that language, the proxi- 

 mate (or lowest) Kind to which any individual is referable, is called 

 its species. Conformably to this. Sir Isaac Newton would be said to 

 be of the species man. There are indeed numerous sub-classes in- 

 cluded in the class man, to which Sir Isaac Newton also belongs ; as, 

 for example, Christian, and Englishman, and Mathematician. But 

 these, though distinct classes, are not, in our sense of the term, distinct 

 Kinds of men. A Christian, for example, differs fixjra other human 

 beings ; but he differs only in the attribute which the word expresses, 

 namely, belief in Christianity, and whatever else that implies, either as 

 involved in the fact itself, or connected with it through some law of 

 cause and effect. We should never think of inquiring what properties, 



