§§64--71. Summary. Cic. much moved thus begins. The strength of Lucullus argument has affected me much, yet I feel that it can be answered. First, however, I must speak something that concerns my character (64). I protest my entire sincerity in all that I say, and would confirm it by an oath, were that proper (65). I am a passionate inquirer after truth, and on that very account hold it disgraceful to assent to what is false. I do not deny that I make slips, but we must deal with the _sapiens_, whose characteristic it is never to err in giving his assent (66). Hear Arcesilas' argument: if the _sapiens_ ever gives his assent he will be obliged to _opine_, but he never will _opine_ therefore he never will give his assent. The Stoics and Antiochus deny the first of these statements, on the ground that it is possible to distinguish between true and false (67). Even if it be so the mere habit of assenting is full of peril. Still, our whole argument must tend to show that _perception_ in the Stoic sense is impossible (68). However, a few words first with Antiochus. When he was converted, what proof had he of the doctrine he had so long denied? (69) Some think he wished to found a school called by his own name. It is more probable that he could no longer bear the opposition of all other schools to the Academy (70). His conversion gave a splendid opening for an _argumentum ad hominem_ (71). §64. _Quadam oratione_: so Halm, also Bait. after the best MSS., not _quandam orationem_ as Lamb., Orelli. _De ipsa re_: cf. _de causa ipsa_ above. _Respondere posse_: for the om. of _me_ before the infin, which has wrongly caused many edd. either to read _respondere_ (as Dav., Bait.) or to insert _me_ (as Lamb.), see n. on I. 7. §65. _Studio certandi_: = φιλονεικια. _Pertinacia ... calumnia_: n. on 14. _Iurarem_: Cic. was thinking of his own famous oath at the end of his consulship.