In philosophy we have important dialogues by Plato, Bishop Berkeley, and David Hume. A dialogue is a great format for presenting opposed points of view, without requiring that the author choose between them. But in art history, apart from some staged scenes in Diderot’s Salons, Mondrian’s dialogues, and Roberto Longhi’s short imagined discussion between Caravaggio and Tiepolo, it’s hard to cite examples of this literary form. (There were some French dialogues preceding modernism, and of...