A three-dimensional object casts a shadow in only two dimensions. From that observation Duchamp concluded that a three-dimensional object must, in turn, be the shadow of another object in four dimensions.

Along these lines, Duchamp has created the image of the Bride as the lunar projection of an invisible form. Yet this transcendental conception was reinforced by his very tactile idea of the fourth dimension, since Duchamp considers the sexual act the pre-eminent fourth-dimensional situation.