Chap. VI. ANTIENT METAPHYSICS. 421 



My only poftulatum, therefore, in this cafe, is fuch, that the 

 greateft fceptic mufi: grant it, namely, * That the evidence of con- 

 ' fcioufnefs is infallible.' It is upon this evidence that Des Cartes 

 was convinced of his own exiftence ; ' jpor,* fays he, * / think ; 

 * therefore I amJ* Now, that he thought, he could not know other- 

 wife than by confcioufnefs. And one Ihould have imagined the fame 

 argument might have convinced Mr Hume of his exiftence, though it 

 feems it did not ; for 1 do not think fo meanly of this argument as 

 fome do : But, on the contrary, I am perfuaded that we cannot be 

 fure of the exiftence of any thing but from its operations. And 

 the only difference in this matter, betwixt our own exiftence and that 

 of other things, is, that we know our own operations by confciouf- 

 nefs : Whereas, the operations of other things, we know only by the 

 information of our fenfes. And he is fo far, likewife, in the right, 

 that he lays the foundation of his phllofophy upon this cleareft of all 

 evidence, being that without which there would be no demonflration 

 or proof of any kind : For, if we were not confcious of having per- 

 ceived the truth of the premiffes, we never could infer the conduiion. 

 -—But, to proceed in our argument. 



It is then admitted, that, by confcioufnefs, we know that we have 

 perceptions of fenfe : By the fame means we know the difference of 

 thofe perceptions ; that the perception of Jeeing, for example, is 

 not the fame with the perception of hearing. And, further, we 

 know, in the fame way, the difference of the fame perception in dif- 

 ferent circumflances. I fee, for example, a jire at fome diftance. 

 This I call the perception of the fenfe. I fhut my eyes, and I ftili 

 have the perception of fire ; but it is a perception, I fay, not from the 

 fenfe, but from the phantafia. And the difference betwixt the two, I 

 know, is, that the one is from within, and the other from without. 

 That the one is from within, I know with the fame certainty that I 

 know 1 have the perception, and, by the fame means, by confciouf- 

 nefs. 



