Thomas Aquinas

“ According to Isidore (Etym. x) , "unwisdom is contrary to wisdom because it lacks the savor of discretion and sense"; so that unwisdom is seemingly the same as folly. Yet a man would appear to be a fool chiefly through some deficiency in the verdict of that judgment, which is according to the highest cause, for if a man fails in judgment about some trivial matter, he is not for that reason called a fool. ”

“ Wherefore it is manifest that "folly" is opposed to "wisdom" as its contrary, while "fatuity" is opposed to it as a pure negation: since the fatuous man lacks the sense of judgment, while the fool has the sense, though dulled, whereas the wise man has the sense acute and penetrating. ”

“ Now a man may in this respect contract dullness in judgment in two ways. First, from a natural indisposition, as in the case of idiots, and such like folly is no sin. Secondly, by plunging his sense into earthly things, whereby his sense is rendered incapable of perceiving Divine things, according to 1 Cor. 2:14, "The sensual man perceiveth not these things that are of the Spirit of God," even as sweet things have no savor for a man whose taste is infected with an evil humor: and such like folly is a sin. ”