I will not pause therefore to prove the necessity of a knowledge without which all other is but doubt and presumption. I will only examine, in a brief digression, if this knowledge is possible. Plato, as I have said, made the whole edifice of his doctrine rest upon it; he taught, according to Socrates, that ignorance of one’s self involves all ignorance, all mistakes, all vices, and all misfortunes; whereas knowledge of one’s self, on the contrary, draws all virtue and all goodness[483]: so that it cannot be doubted that this knowledge might be considered possible, since its impossibility merely questioned would render its system null and void. However, as Socrates had said that he knew nothing, in order to distinguish himself from the sophists of his day who pretended to know everything; as Plato had constantly used in his teachings that sort of dialectic which, proceeding toward truth by doubt, consists in defining things for what they are, knowing their essence, distinguishing those which are real from those which are only illusory; and above all as the favourite maxim of these two philosophers had been that it was necessary to renounce all manner of prejudices, not pretending to know that of which one is ignorant, and giving assent only to clear and evident truths; it came to pass that the disciples of these great men, having lost sight of the real spirit of their doctrine, took the means for the end; and imagining that the perfection of wisdom was in the doubt which leads to it, established as fundamental maxim, that the wise man ought neither to affirm nor deny anything; but to hold his assent suspended between the _pro_ and _con_ of each thing.[484] Arcesilaus, who declared himself the chief of this revolution, was a man of vast intellect, endowed with much physical and moral means, an imposing presence, and very eloquent,[485] but imbued with that secret terror which prevents concentrating upon the things that one regards as sacred and forbidden; audacious and almost impious to all outward appearance, he was, in reality, timid and superstitious.[486] Impressed with the inadequacy of his researches to discover the certainty of certain principles, his vanity had persuaded him that this certainty was undiscoverable, since he, Arcesilaus, did not find it; and his superstition acting in accord with his vanity, he finally believed that the ignorance of man is an effect of the will of God; and that, according to the meaning of a passage from Hesiod that he cited unceasingly, the Divinity has spread an impenetrable veil between it and the human understanding.[487] Also he named the effect of this ignorance, _Acatalepsy_, that is to say incomprehensibility, or impossibility to raise the veil.[488] His disciples in great numbers adopted this incomprehensibility and applied it to all sorts of subjects; now denying, then affirming the same thing; placing a principle, and overthrowing it the next moment; becoming entangled