“[In 1970] I happened to overhear a young painter say, ‘I still don’t get it, why would anyone want to draw on the wall?’ Although we might smile at his question after everything that has happened in art over the last forty years, the idea of an ephemeral artwork was anathema to every belief system then current. … But the real question was, and still is, this: what led [1960’s] artists to take the radical step of abandoning traditional supports and begin working directly on the wall? … The argument as I saw it … went in another direction. … Thickness, ‘the obstinate chunkiness of the third dimension,” is what makes objects objects. But a difficult problem remained: how do you do that? … Simultaneously, in front of and behind you, fixed where they are by the wall’s mass, they become, perceptually, pure surface. … These works cannot be held; they can only be seen.”