I have seen mad people, and I have known some who were quite intelligent, lucid, even clear-sighted in every concern of life, except on one point. They could speak clearly, readily, profoundly on everything; till their thoughts were caught in the breakers of their delusions and went to pieces there, were dispersed and swamped in that furious and terrible sea of fogs and squalls which is called MADNESS.

Boule de Sulf, and other stories (ed. 1909)