The Museum of Modern Art has an impressive Marcel Duchamp show right now, and Gagosian is showing him , too. What can one still say about him that hasn’t been said? Let’s see. I come to Duchamp with an unfair advantage. I’ve owned a few good pieces, and I’ve been able to actually see what they’re like to live with. Wind back the clock to an auction not that long ago. Remember when 14 of Duchamp’s readymades—a complete set—were up for sale back in 2002 at Phillips de Pury and Luxembourg ? A young woman at the New York auction house was trying to get me interested in these works, which Duchamp had editioned via dealer Arturo Schwartz in 1964. Why make editions of long-lost pieces from the 1910s? Walter Hopps ‘s Duchamp retrospective at the Pasadena Art Museum in 1963 had struck a chord with artists and the cognoscenti. Arturo sensed that the timing was right, and Marcel wasn’t averse to the money at that point, since he had probably been living on thin air for a while.…