6o ANTIENT METAPHYSICS. Book 11. 



From what is here faid, it is ftill further evident, that what I ob- 

 ferved was true, ' that we have no perfect idea of any natural fub- 

 * ftance:' For it now appears, that wc have no diJiin^t comprehen- 

 fion of the ejfential form of any fuch fubftance, any more than of the 

 fnatter. Nor is this to be wondered at ; for, in ihejirfi place, it is im- 

 poffible that we can perceive by our fenfes this interjial form^ any more 

 than the matter^ diverted of all the cjualities which affe^ our fenfes. 

 And, fecondly^ It is as impoffible that either of them fhould be per- 

 :fe(Sl]y comprehended by our intelled:, unlefs we could fuppofe, that 

 the ideas of our minds are as perfect as thofe of the Divine, 



If this wanted any further proof, it is evident from the way in 

 which we form definitions of any fuch fubftance : It is from quali- 

 ties of them which are perceptible by our fenfes ; for it is a combina- 

 tion of a certain number of fuch qualities, united together in a certain 

 matter as a fuhflratum^ which conflitutes our ideas of all natural fub- 

 ftances. Now, what are thefe qualities ? They are no other but qua- 

 lities which the natural fubftance has in common with thofe of the 

 fame kind and thofe of the fame fpecies : For, though definition is 

 very properly faid by Ariftotle to confift of the genus and the fpecifw 

 difference^ yet that fpecific difference is no other than the qualities 

 which every individual of the fpecies has in common with other indi- 

 viduals of the fame fpecies, in thf fame manner as the genus is con- 

 ftituted of all thofe qualities whichi he individual has in common with 

 thofe of the fame genus. So that the qualities which conftitute the 

 fpecies, are called differential qualities^ only becaufe they diftinguifh 

 the fpecies from other fpeciefes of the fame genus; for, in reality, 

 they are all finiihtudes ; and the truth is, that the intelle6l perceives 

 nothing but by fimilitudes, as I have elfewhere obferved *. Now, 

 every individual fubftance, befides what is common to other things, 



muft: 



* Origin and Progrefs of Language, vol. i. book i. chap. 6. page 68. 69. 70. 

 and 71. 



