Marcel Duchamp once asked whether it is possible to make something that is not a work of art. This question returns over and over in modernist culture, where there are no longer any authoritative criteria for what can be identified (or excluded) as a work of art. As William Carlos Williams says, "A poem can be made of anything," even newspaper clippings. At this point, art turns into philosophy, all art is now conceptual art, and the manifesto becomes...