“In the second place,” says Arcesilaus, “there is no apprehended conception that is not also false, as has been confirmed many times and oft,” just as the Stoics themselves say that the apprehended conception could be both true and false. Determinate content has its opposite in a determinate which must likewise as an object of thought be true; and this destroys itself. In this consists the blind wandering about in thoughts and reasons such as these, which are not grasped as Idea, as the unity of opposites, but in one of the opposites asserts one thing, and then, with as good reason, the opposite. The truth of the world is, on the contrary, quite different, the universal law of reason which is as such for thought. Reasons are relatively ultimate for a content, but not absolutely ultimate; they can only be regarded as good reasons, as probability, as the Academics express it. This is a great truth which Arcesilaus had attained. But because no unity can thus come forth, he then draws the conclusion that the wise man must withhold his assent, that is, not that he should not think, but that he must not merely for that reason regard as true that which is thought. “For since nothing is comprehensible, he will, if he assents, assent to an incomprehensible; now because such an assent is opinion, the wise man will only be wise in opinion.”[172] We still likewise hear this said: Man thinks, but does not thereby arrive at the truth; it remains beyond. Cicero (Acad. Quæst. IV. 24) thus expresses this: “Neither the false nor the true can be known, if the true were simply to be such as is the false.”
_b._ In relation to what is practical, Arcesilaus says: “But since the conduct of life without a criterion of the true or the false is impossible, and the end of life, or happiness, can only be determined through such grounds, the wise man, not withholding his approbation regarding everything, will, as regards what has to be done and left undone, direct his actions in accordance with the probable (εὔλογον),” as the subjectively convincing conception. What is right in this is that the good ground does not extend as far as truth. “Happiness is brought about by discretion (φρόνησις), and rational conduct operates in fitting and right action (κατορθώμασι); that is rightly done which is permitted by a well-grounded justification,” so that it appears to be true. “Thus, he who regards what is well-founded will do rightly and be happy,” but for this culture and intelligent thought are requisite. Arcesilaus thus remains at the indeterminate, at subjectivity of conviction, and a probability justified by good grounds. Thus we see that in regard to what is positive, Arcesilaus does not really get any further than the Stoics, nor say anything different from what they do; only the form is different, because, what the Stoics call true, Arcesilaus calls well-founded or probable. But, on the whole, he possessed a higher kind of knowledge than the Stoics, because what is thus founded cannot be held to have the significance of an implicit existence, but only a relative truth in consciousness.