  One further issue concerning Descartes’s general account of the nature of the mind-body union, which Desgabets raised in order to dispel, concerns the common complaint that the Cartesian view fails to account for the interaction of material and immaterial substances. Desgabets did not regard this as a true problem because he thought that the question demanded the impossible—an explanation of how the organized body and reasonable soul, which are in fact made for each other, can exercise a mutual commerce. He likened this to asking an artisan to explain how the convex surface of a peg can possibly fill that of a concave hole. It is akin to asking why extension is the essence of body, or why thought is the essence of mind. It’s just the way God made the world.