394 ANTIENT METAPHYSICS. Book V. 



ved *, any perception of truth ; for, though they have true percep- 

 tions, and perceive alfo the relations betwixt thofe perceptions, yet 

 they do not perceive that they perceive^ and, confequently, have no 

 perception of truth. The neceffity of this reflex adt of the mind is 

 moft apparent in fyllogiftical truth ; for, if a nnan is not confcious of 

 the truth of tlie two premifTes of a fyllogifm, and does not refled, 

 or, as it were, look back upon them,, he cannot proceed to infer the 

 conclufion. 



Thofe, who have ftudied mathematics much, and no other fcience, 

 are apt to grow fo fond of them, as to believe that there is no cer- 

 tainty in any other fcience, or any other axioms except thofe of Eu- 

 clid. But, if they were philofophers, and could fee the whole extent 

 of the objeds of human knowledge! they would know, that fcience is 

 not confined to one of the categories, viz. quantity, but that there are 

 axioms and demonftrations belonging to every one of the categories^ 

 and fome to all of them in general, particularly one mentioned by 

 Ariflotle f, viz. * That it is impojQTible the fame thing can be, and not 

 * be, at the fame time, and in the fame refpedt.* This is the moft 

 univerfal of all the axioms, and the moft certain, fays Ariftotle, of 

 all the principles J. It is, indeed, the foundation of all truth, and 



all 



* Ov '*>( uXiiSovf umXYiVT tKTi n uXcyaf yvats-Hy «AA«{ fttftv t*v T^nytietrtiy ivTriP xect la-Ti 

 ixvTfit yfmctmif Tig; in xwrt tovtc ynucrKU i}\Uf i; in (tXyi6i>fy ri ye&fliw; MfTMijyojccEV);;* *vtj^ 



y«5 HivTJii" yvuTiTm, SimpUcU Comment, ad lib. 1' Arijistelii de Jnimay feU 57. And 

 he adds, what is certainly true, that the brute is wholly converfant with external 

 things, without attending to any thing that pafles within himfelf; and therefore he 

 has no notion of truth in fpeculation. Neither in practice has he any knowledge of 

 what is good or ///, (for that alfo is acquired by refte(^ion alone), but only of what is 

 pleafant and difagreeable. 

 t Metaph lib. 4. cap. 4. 



