ON HUMAN UNDERSTANDING. S5? 



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 INDENTITY, 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 I neither can prove nor 

 want to prove. 1 do not want to prove it, for I know it with certain know- 

 ledge, or, in other words, it is SELF-EVIDENT. 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 agreement 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 I 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 depends 

 upon the constant agreement of the idea with itself the agreement of identity. 



Nothing has been productive of more mischief in the science of metaphy- 

 sics than this absurd restlessness in seeking after proofs in cases of intuition, 

 where no proofs are to be had, and the knowledge is certain without them. 

 M. Des Cartes's 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 particularly those of Bishop Berkeley 

 and Mr. Hume, has equally proved the ruin of these. When 1 affirm that 7 

 am, I affirm that of which I have an intuitive knowledge : and when I affirm, 

 that I think, I only make a proposition of the same kind. The connexion be- 

 tween the two ideas I am, and the two ideas I think, is a connexion of coexist- 

 ence 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 absur- 

 dities of M. Des Cartes's argument, / think, 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 Iain without 

 thinking, than it can put together the two ideas / think, without being. But 

 nothing is gained by their being put together in the way of proof or demon- 

 stration ; for I have no more evidence of my existence by calling up the ideas 

 I think, than I had before this proposition was conceived; and hence the 

 attempt not only fails, but could lead to no use if it could stand its ground. 



Our knowledge of personal identity is derived from the same source. It 

 is INTUITIVE. This is a subject which has excited a great deal of learned 

 controversy, and called forth many a different proof, or attempt at proof, 

 from the different disputants who have engaged in it. Mr. Locke himself, 

 with a singular deviation from the principles of his own system, has fallen 

 into a common error and offered as a proof the idea of consciousness. No 

 proof, however, or attempt at proof, is more imperfect ; for the identity often 

 continues when the consciousness is interrupted, as in sleep without dreaming, 

 in apoplexy, catalepsy, drowning, and various other cases : and hence, if identity 

 were dependent on consciousness, the same man in a dead sleep and out of it 

 would be two or more different persons. The truth is, that our knowledge of 

 identity is intuitive; the two ideas 7am, and the two ideas I was, a combina- 

 tion of which constitutes the more complex idea of personal identity, are ideas 

 of necessary connexion from the first moment the connexion can be formed: 

 and hence they produce certain knowledge, and can have no proof; since 



