“Thus we better understand the curious implication assigned to the navigation of madmen and the prestige attending it. On the one hand, we must not minimize its incontestable practical effectiveness: to hand a madman over to sailors was to be permanently sure he would not be prowling beneath the city walls; it made sure that he would go far away; it made him a prisoner of his own departure. But water adds to this the dark mass of its own values; it carries off, but it does more: it purifies. Navigation delivers man to the uncertainty of fate; on water, each of us is in the hands of his own destiny; every embarkation is, potentially, the last.
It is for the other world that the madman sets sail in his fools’ boat; it is from the other world that he comes when he disembarks. The madman’s voyage is at once a rigorous division and an absolute Passage. In one sense, it simply develops, across a half-real, half-imaginary geography, the madman’s liminal position on the horizon of medieval concern—a position symbolized and made real at the same time by the madman’s privilege of being confined within the city gates: his exclusion must enclose him; if he cannot and must not have another prison than the threshold itself, he is kept at the point of passage. He is put in the interior and exterior, and inversely.
A highly symbolic position, which will doubtless remain his until our own day, if we are willing to admit that what was formerly a visible fortress of order has now become the castle of our conscience.” – Michel Foucault, from Madness and Civilization