The forh dimension (M. Duchamp 1966)

Simply, I thought of the idea of a projection, of an invisible fourth dimension, something you couldn't see with your eyes. Since I found that one could make a cast shadow from a three dimensional thing, any object whatsoever - just as the projecting of the sun on the earth makes two dimensions - I thought that, by simple intellectual analogy, the fourth dimension could project an object of three dimensions, or, to put it another way, any three-dimensional object, which we see dispassionately, is a projection of something four-dimensional, something we are not familiar with.

Pure chance interested me as a way of going against logical reality: to put something on a canvas, on a bit of paper, to associate the idea of a perpendicular thread a meter long falling from the height of one meter onto a horizontal plane, making its own deformation.

Marcel Duchamp. 1966.
Pierre Cabanne. Dialogues with Marchel Duchamp. Thames and Hudson 1971.