Apuleius, Apologia 80
“Finally, what do you prefer that she was sane or insane while she was writing? You claim sane? Therefore, she was not under the influence of occult arts. You will say she was insane? In that case, she was unconscious of what she wrote and must not be trusted. Or, more to the case, if she had been insane, she would not have known that she was insane.
For, it is like when someone is not silent because he says he is silent and by the utterance itself undermines his own claim. But saying “I’m crazy” betrays someone even more because it is not true unless he says it without understanding. The person is sane, moreover, who knows what insanity is; and, certainly, insanity cannot know itself any more than blindness can see itself.
Therefore, Prudentilla was sound in mind, if she did not think she was sound in mind. I could add more, if I wanted to, but I will leave philosopher behind now.”
Postremo quid vis: sanam an insanam fuisse, dum scriberet? Sanam dices? Nihil ergo erat magicis artibus passa. Insanam respondebis? Nesciit ergo quid scripserit, eoque ei fides non habenda est; immo etiam, si fuisset insana, insanam se esse nescisset. Nam ut absurde facit qui tacere se dicit, quod ibidem dicendo tacere sese non tacet et ipsa professione quod profitetur infirmat, ita vel magis hoc repugnant, “ego insanio,” quod verum non est, nisi sciens dicit. Porro sanus est, qui scit quid sit insania, quippe insania scire se non potest, non magis quam caecitas se videre; igitur Pudentilla compos mentis fuit, si compotem mentis se non putabat. Possum, si velim, pluribus, sed mitto dialectica