Why do critics insist on comparing one artist with another? More to the point -- why do I do it so obsessively? I have just published a review of two artists showing at this year's Edinburgh festival. Although Martin Creed and Richard Wright are both showing in the same city at its most crowded cultural season, that does not make them competitors -- surely? Well, that's how I see them. My article today sets up a rivalry, and seems to assume that to love Wright as I do, it is necessary to disparage Creed.