DBS CARTES'S MAXIM UNSOUND. 29 



into the too hasty adoption of trite and current maxims, 

 however prevalent they may be. Let these, also, be care- 

 fully scrutinized, to ascertain whether or not some specious 

 sophism may not lurk beneath them. To cite a striking 

 example : A maxim of this kind, which lies at the 

 basis of the Cartesian philosophy, and which for some 

 time was almost universally received, was couched in the 

 terms, "Ego cogito, ergo sum / think, therefore I exist"* 

 This being expressed with epigrammatic point and 

 terseness, aptly insinuates itself into the mind ; yet it is 

 palpably a sophism, a petitio principii. The very thing 

 to be proved by it is taken for granted ; for there cannot 

 be thought unless the thinking being exist : and thus, 

 in order to know that / think, I must first be persuaded 

 that I exist; and, of course, to prove the fact of my 

 existence by that of my thinking, is to reason in a circle. 

 It is, in truth, equally evident that I think and that 

 I exist ; so that there is here no proof: and yet this 

 example of false reasoning was worked into the very 

 foundation of a philosophical system, which for a long 

 time prevailed more universally than that of Newton. 



* When I delivered this lecture, I participated in what, so far as I knew, 

 was the general belief, that Des Cartes was the author of this celebrated 

 enthymeme. But I have since found that a kindred maxim, expressed in 

 less objectionable terms, occurs so early as in the works of St. Augustine. 

 In opposing the Sceptics of his time, he says, " I do not perceive what 

 mighty force there is in the scepticism of the Academics. For my part, I 

 look upon it as a very just observation of theirs, that we may deceive 

 ourselves. But if I deceive myself, may I not thence conclude that I am? 

 For he who has no existence cannot deceive himself; wherefore, by that 

 very circumstance, that I deceive myself, I find that I am." August, de 

 Lib. Arbit. 1. ii. cap. 3. Probably this passage had been read by Des Cartes 

 during his early studies under the Jesuits ; and occurred to him afresh, 

 long afterwards, with the modification it has received in his hands, without 

 his being at all conscious that it was a modified reminiscence, and not an 

 original thought. 



