Chap. IV. ANTIENT METAPHYSICS. 405 



clples ; and each of thefe Is twofold. The former Is txihtv from pr'm- 

 ciples felt-evident, or from propofitions already demonftrated. Again, 

 the reafoning to the principles does either eftabliili thofe principles, or 

 overturn them. If it eftablifh tliem, it is analyfis, which I have al- 

 ready explained ; and it is oppofed \.oJyntheJis^ by which we defcend 

 from the principles which we have difcovered by the analyfis^ and, in 

 that way, demonftrate a priori. If, on the other hand, it overturn 

 the principles, then it is what is called apagogical realoning, or a re- 

 duction to what is abfurd or impoffible. This happens, v^hen we fup- 

 pofe, as I have faid, the contrary of what is propofed to be proved, 

 and (how that fuch a fuppofition is neceflarily conneded with fome- 

 thing that is abfurd or impoifible. 



This is the nature of demonftrative and fcientifical reafoning. But 

 there is another kind of realoning, which was much pra6tifed, even 

 by philofophers in antient times, and was always, and is ftill the chief 

 kind of reafoning ufed by rhetoricians and public fpeakers, being al- 

 mofl the only kind of reafoning that can be underftood by the/»^o- 

 />/(?, that is, by men who are not taught or inftruded. It was called 

 dialefiic by Ariftotle ; but it is to be obferved, that his dialeciic is 

 very different from the dialeElic of his mailer Plato, which was en- 

 tirely of the metaphyftcal kind, being deduced from the higheft and 

 moft univerfal principles. Plato, at the fame time, knew very well 

 the dialeciic of Ariftotle, and has praCtifed it very much ; nor was 

 there any kind of reafoning more in falhion at that time, being ufed, 

 not only by the orators, but by the fophifts, who, not having fcience, 

 and,confeqaently, not being able to argue from the nature of the thing, 

 argued dialefUcatly. Bur it was not reduced to an art, till Ariftotle,. 

 to whom arts, as well as philofophy, have been fo much obliged) com- 

 pofed his books of topics. 



It 



