400 



ON HUMAN UNDERSTANDING. 



happens far more generally that the agreement or disagreement is by ne 

 means obvious ; and we are obliged, as in the case of circumstantial evi- 

 dence, to look out for some intermediate idea, which the schools denomi- 

 nate a medius terminus^ by which the separate ideas maybe united. To 

 make this research is the peculiar province of the discursive faculty of 

 reason ; and hence the information thus obtained is called rational 



KNOWLEDGE. 



Let us take a brief view of both these. When I affirm that white is 

 not black ; or, which is a proposition of the same kind, that white is white, 

 and black is black, I affirm what I know intuitively. The colours of white 

 and of black, have excited ideas in my mind, which, whenever they occur, 

 must be identic and true to_ themselves ; for it is not possible for me to 

 have any other idea of white than white, or of black than black : the 

 agreement in this case is the agreement of identity, the agreement of 

 either idea with itself : and hence the man who asks me to prove that 

 white is white, or that white is not black, or red, or yellow, asks me to 

 prove what 1 neither can prove nor want to prove. \ do not want to prove 

 it, for I know it with certain knowledge, or, in other words, it is self-evi- 

 dent. And I cannot prove it for this reason : that every proof consists 

 in placing between two ideas that we want to unite together by an agree- 

 ment which we do not perceive, an idea whose agreement with both of 

 them is more obvious. But what idea can I place by the side of the idea 

 of white, of black, of red, or of yellow, that can agree more fully with 

 either of these ideas, than such ideas agree with themselves ? Every one 

 must see that there is no such idea to be had; and consequently that 1 can 

 neither offer a proof nor want one. And the very attempt to obtain such 

 a proof would be an absurdity ; for could it possibly be acquired, it would 

 not add to my knowledge, which is perfect and certain already, and de- 

 pends upon the constant agreement of the idea with itself, — the agreement 

 of identity. 



Nothing has been productive of mor^ mischief in the science of meta- 

 physics than this absurd restlessness in seeking after proofs in cases of in- 

 tuition, where no proofs are to be had, and the knowledge is certain 

 without them. M. des Cartes' hypothesis, as I had occasion to notice 

 in our last lecture, commences with an instance of this very absurdity, 

 and it has proved the ruin of it ; and the same attempt in various other 

 hypotheses of later date that we shall yet have to touch upon, and par- 

 ticularly those of Bishop Berkeley and Mr. Hume, has equally proved 

 the ruin of these. When I affirm that / am, I affirm that of which 1 have 

 an intuitive knowledge t and when I affirm that / thinks I only make a 

 proposition of the same kind. The connexion between the two ideas, J 

 am, and the two ideas / thinks is a connexion of co-existence or absolute 

 necessity. It is not possible to separate them, and they want no third or 

 intervening idea to unite them ; for if it were possible for me to doubt 

 whether I thought, or whether I existed, the very doubt itself would answer 

 the purpose of a proof in either case. Now one of the chief absurdities 

 of M, des Cartes' argument, / thinks therefore I am^ consists in his put- 

 ting two propositions equally self-evident and intuitive, by the side of each 

 other, and making the first the proof of the second. For being equally 

 intuitive, the second must be just as good a proof of the first as the first is 

 of the second ; since the mind can no more put together the two ideas lam 

 without thinkings than it can put together the two ideas / think, without 

 heing. But nothing is gained by their being put together in the way of 



