This connection of the New Academy with Stoicism can be proved in the case of its first founder, [1424] Arcesilaus. [1425] The doubts of this philosopher are directed not only to knowledge derived from the senses, but to rational knowledge as well. [1426] The principal object of his attack was, however, the Stoic theory of irresistible impressions; [1427] and in overthrowing that theory Arcesilaus, it would seem, believed he had exploded every possibility of rational knowledge; for the Stoic appeal to the senses he regarded as the only possible form of a theory of knowledge, and the theories of Plato and Aristotle he ignored altogether. Indeed, no peculiar arguments against knowledge are referred to him. The old sceptical arguments of Plato and Socrates, of Anaxagoras, Empedocles, Democritus, Heraclitus, and Parmenides, are repeated, [1428] all of which apply only to the knowledge of the senses, and not to rational knowledge. Nevertheless, Arcesilaus aimed at overthrowing the latter along with the former. [1429] The opinion that he only used doubt to prepare for or to conceal genuine Platonism, [1430] is opposed to all credible authorities. It appears, however, established that he deemed it unnecessary to refute the theory of a knowledge existing independently of the senses. The Stoic arguments in favour of irresistible impressions Arcesilaus met by asserting that an intermediate something between knowledge and opinion, a kind of conviction common to the wise and the unwise, such as the Stoic κατάληψις, is inconceivable; the wise man’s conviction is always knowledge, that of the fool is always opinion. [1431] Going then farther into the idea of φαντασία καταληπτική, he endeavoured to show that it contained an internal contradiction; for to conceive (κατάληψις) is to approve (συγκατάθεσις), and approval never applies to sensation, but only to thoughts and general ideas. [1432] Lastly, if the Stoics regarded force of conviction as the distinctive mark of a true or irresistible conception, and as belonging to it in distinction from every other, the Sceptic rejoined that such conceptions do not exist, and that no true conception is of such a nature, but that a false one may be equally irresistible. [1433] If no certainty of perception is possible, no knowledge is possible. [1434] And since the wise man—for on this point Arcesilaus agrees with the Stoics—must only consider knowledge, and not opinion, nothing remains for him but to abstain from all and every statement, and to despair of any certain conviction. [1435] It is therefore impossible to know anything, nor can we even know for certain that we do not know anything. [1436] It was quite in accordance with this theory for Arcesilaus to lay down no definite view in his lectures, but only to refute the views of others. [1437] Even his disparaging remarks on dialectic, [1438] supposing them to be genuine, [1439] are not at variance with this conduct. He might