Arcesilaus left no writings, and his criticisms on the Stoic theory, as reported by Cicero and Sextus Empiricus, have a somewhat unsatisfactory appearance. By what we can make out, he seems to have insisted on the infallibility of the wise man to a much greater extent than the Stoics themselves, not allowing that there was any class of judgments in which he was liable to be mistaken. But just as the Stoics were obliged to accept suicide as an indispensable safeguard for the inviolability of their personal dignity and happiness, so also Arcesilaus had recourse to a kind of intellectual suicide for the purpose of securing immunity from error. The only way, according to him, in which the sage can make sure of never being mistaken is never to be certain about anything. For, granting that every mental representation is produced by a corresponding object in the external world, still different objects are connected by such a number of insensible gradations that the impressions produced by them are virtually indistinguishable from one another; while a fertile source of illusions also exists in the diversity of impressions produced by the same object acting on different senses and at different times. Moreover, the Stoics themselves admitted that the sage might form a mistaken opinion; it was only for his convictions that they claimed unerring accuracy, each of the two—opinion and conviction—being the product of a distinct intellectual energy. Here again, Arcesilaus employed his method of infinitesimal transitions, refusing to admit that the various cognitive faculties could be separated by any hard and fast line; especially as, according to the theory then held by all parties, and by none more strongly than the Stoics, intellectual conceptions are derived exclusively from the data of sense and imagination. We can see that the logic of Scepticism is, equally with that of the other Greek systems, determined by the three fundamental moments of Greek thought. There is first the careful circumscription of certainty; then there is the mediating process by which it is insensibly connected with error; and, lastly, as a result of this process, there is the antithetical opposition of a negative to an affirmative proposition on every possible subject of mental representation.[231]