are of that kind that one can only see the fact in one’s mind, others such that one can design and effect something, how can a geometrician perceive those things which have no existence, or which cannot be distinguished from what is false? or how can he who plays on the lyre complete his rhythm, and finish verses? And the same will be the case with respect to similar arts, whose whole work consists in acting and in effecting something. For what is there that can be effected by art, unless the man who exercises the art has many perceptions? VIII. And most especially does the knowledge of virtues confirm the assertion that many things can be perceived and comprehended. And in those things alone do we say that science exists; which we consider to be not a mere comprehension of things, but one that is firm and unchangeable; and we consider it also to be wisdom, the art of living which, by itself, derives consistency from itself. But if that consistency has no perception or knowledge about it, then I ask whence it has originated and how? I ask also, why that good man who has made up his mind to endure every kind of torture, to be torn by intolerable pain, rather than to betray his duty or his faith, has imposed on himself such bitter conditions, when he has nothing comprehended, perceived, known, or established, to lead him to think that he is bound to do so? It cannot, then, by any possibility be the case that any one should estimate equity and good faith so highly as to shrink from no punishment for the sake of preserving them, unless he has assented to those facts which cannot be false. But as to wisdom itself, if it be ignorant of its own character, and if it does not know whether it be wisdom or not, in the first place, how is it to obtain its name of wisdom? Secondly, how will it venture to undertake any exploit, or to perform it with confidence, when it has nothing certain to follow? But when it doubts what is the chief and highest good, being ignorant to what everything is referred, how can it be wisdom? And that also is manifest, that it is necessary that there should be laid down in the first place a principle which wisdom may follow when it begins to act; and that principle must be adapted to nature. For otherwise, the desire, (for that is how I translate ὁρμὴ,) by which we are impelled to act, and by which we desire what has been seen, cannot be set in motion. But that which sets anything in motion must first be seen and trusted, which cannot be the case if that which is seen cannot be distinguished from what is false. But how can the mind be moved to desire anything, if it cannot be perceived whether that which is seen is adapted to nature or inconsistent with it?