214 u Cogito, ergo sum" CHAP. 



be asked until the self exists to ask it; so that its 

 denial would not only contradict an affirmation of 

 Consciousness, but would also contradict that logical 

 principle which lies at the base of all reasoning, and 

 indeed of all assertion, that a contradiction cannot be 

 true that a thing cannot at once be existent and 

 non-existent, and a proposition cannot be at once 

 true and false. This is not offered as a new demon- 

 stration ; it is only a restatement of that funda- 

 mental axiom of all philosophy which Descartes 

 formulated in the words "Cogito, ergo sum," "I 

 think, therefore I exist"; that is to say, the 

 existence of self is made known and proved, not in 

 mere Sensation but in Thought. It seems to me that 

 this saying is improved by translating it into English, 

 and thus bringing into prominence the personal 

 pronoun. 1 



Physical and metaphysical knowledge are both 

 equally real ; and as metaphysical knowledge, or 

 knowledge of what is made known in Consciousness, 

 begins with the consciousness of self, so physical 

 knowledge, or knowledge of external nature, begins 

 with the discovery of the existence of a world 



1 It has been said that this is not a proof but a petitio 

 principii, because it involves the assumption that whatever 

 thinks must exist. But this mistakes the true significance of 

 Descartes' saying. It is not meant as logical demonstration, 

 but goes deeper than demonstration. In demonstration, from 

 truths already known we infer other truths ; but this saying 

 is merely a statement of the way in which, as a matter of fact, 

 the self becomes aware of itself as a self. 



