The artist thinks outside the box but retains a relationship to the box. The psychotic has lost the box.
Actually I do think there is a relationship. It is not a direct line or a simple cause and effect but a kind of webwork of continuums on each of which there is a “normal” and an “extreme” range.
Insanity does not confer talent on someone who never had any; and art does not necessarily lead to madness. But there is an aspect of creativity, not just world-class creativity but ordinary weekend-artist creativity, that seems to have something in common with psychosis. Both involve coloring outside the lines. There seems to be a passionate conviction, a commitment to something that isn’t real or meaningful to others, and above all a way of seeing that is not what one has been taught and is different from that of one’s fellows.
I do believe that the creative act has to involve a concept and deliberate intent; it is not just random. Ravings aren’t poetry, and wild scribbles are not art.
I also think a perfectly sane person can be creative, and have a concept, and execute it with intent, and still not make art. It isn’t just an act of will; in fact, it is not altogether voluntary, and perhaps that is where the madness creeps in.