172 NAMES AND PROPOSITIONS. 



(or rationality, for it is of no consequence whether 

 we use the concrete or the abstract form) is generally 

 assigned by logicians as the Differentia; and doubtless 

 this attribute serves the purpose of distinction: but it 

 has also been remarked of man, that he is a cooking 

 animal; the only animal that dresses its food. This, 

 therefore, is another of the attributes by which the 

 species man is distinguished from other species of the 

 same genus : would this attribute serve equally well 

 for a differentia ? The Aristotelians say No ; having 

 laid it down that the differentia must, like the genus 

 and species , be of the essence of the subject. 



And here we lose even that vestige of a meaning 

 grounded in the nature of the things themselves, 

 which may be supposed to be attached to the word 

 essence when it is said that genus and species must 

 be of the essence of the thing. There can be no 

 doubt that when the schoolmen talked of the essences 

 of things as opposed to their accidents, they had 

 confusedly in view the distinction between differences 

 of kind, and the differences which are not of kind ; 

 they meant to intimate that genera and species must 

 be Kinds. Their notion of the essence of a thing was 

 a vague notion of a something which makes it what 

 it is, i. e. y which makes it the Kind of thing that it is 

 which causes it to have all that variety of properties 

 which distinguish its Kind. But when the matter 

 came to be looked at more closely, nobody could 

 discover what caused the thing to have all those 

 properties, nor even that there was anything which 

 caused it to have them. Logicians, however, not 

 liking to admit this, and being unable to detect what 

 made the thing to be what it was, satisfied themselves 

 with what made it to be what it was called. Of the 

 innumerable properties, known and unknown, that are 



