The academic world that I first encountered was one of both intellectual beauty and profound flaws. I was taught at Princeton, in the early 1960s—in history and literature, above all—before the congeries that we term “the Sixties” began. Most of my professors were probably men of the Left—that’s what the surveys tell me—but that fact was never apparent to me, because, except in rare cases, their politics or even their ideological leanings were not inferable from their teaching or syllabi. Reasoned and informed dissent from professorial devil’s advocacy or interpretation was encouraged and rewarded, including challenges to the very terms of an examination question. In retrospect, professors who must have disagreed fundamentally with works such as David Donald’s Lincoln Reconsidered (with its celebrated explanation of the abolitionists’ contempt for Lincoln in terms of the loss of status ...