But if I assume that there is actually nothing which can be perceived, and if I also take what you grant me, that a wise man is never guided by opinion, then the consequence will be that the wise man will restrain all assent on his part; so that you must consider whether you would rather have it so, or let the wise man sometimes form opinions. You do not approve of either, you will say. Let us, then, endeavour to prove that nothing can be perceived; for that is what the whole controversy turns upon. XXII. But first I must say a few words to Antiochus; who under Philo learnt this very doctrine which I am now defending, for such a length of time, that it is certain that no one was ever longer studying it; and who wrote on these subjects with the greatest acuteness, and who yet attacked it in his old age with no less energy than he had defended it in his youth. Although therefore he may have been a shrewd arguer, as indeed he was, still his authority is diminished by his inconsistency. For what day, I should like to know, will ever dawn, which shall reveal to him that distinctive characteristic of what is true and what is false, of which for so many years he denied the existence? Has he devised anything new? He says the same that the Stoics say. Does he repent of having held such an opinion? Why did he not cross over to some other school, and especially to the Stoics? for this disagreement with the Academy was peculiarly theirs. What? did he repent of Mnesarchus or Dardanus, who at that time were the chiefs of the Stoics at Athens? He never deserted Philo till after the time when he himself began to have pupils.