i8o ANTIENT METAPHYSICS. BookIL 



quire to make a mind *. This demonftration is of the kind which 

 the mathematicians call ab ahfurdo^ that is, from the abfurd confe- 

 quences which would follow, if we (hould fuppofe the contrary to be 

 true. Now, though this kind of demonftration be not, properly 

 fpeaking, a priori^ nor fo inftrudive as that which argues from caiife 

 to effe^^ and ihows, not only that the thing is true, hut why it is 

 true ; yet it equally proves the proportion ; and therefore is as con- 

 vincing. 



* This is an argument of Plotinus, in his Eneads, p. 460- as mentioned by Cud- 

 worth in his Intellectual Syflem, p 823. 



CHAP, 



