THERE is nothing that concentrates the mind on an issue more sharply than discovering one has been wrong about it. Twenty years ago, in an article in The Public Interest, I dealt with the subject of the continuing concentration of blacks in American cities and their separation in residence from whites.* The article was occasioned by Anthony Downs’s 1973 book, Opening Up the Suburbs: An Urban Strategy for America. (This article, in expanded form, became part of my 1975 book, Affirmative Discrimination: Ethnic Inequality and Public Policy.) This apparently historically unique degree of concentration—one could call it “segregation,” but I would prefer to reserve that term for state-imposed separation—had been well documented in research of the 1950s and 1960s, and was already under attack in the 1960s and 1970s by a variety of new federal policies, legislative, administrative, and judicial. Anthony Downs had even more extensive policies to propose.