“Clement Greenberg and Virgil Thomson were critics of the first rank. Indeed, Mr. Greenberg was one of the most deservedly influential art critics of the 20th century, while Mr. Thomson is generally regarded as the finest classical-music critic ever to have written for a U.S. newspaper. The world of art would be the poorer had they chosen not to write about it—but for as long as their work is read, some people will wonder whether they could be bought…”