THINKING THE TWENTIETH CENTURY, by Tony Judt with Timothy Snyder. Penguin, 2013, 432 pp. $18 (paperback)

Fame came too late for Tony Judt. He was 57 in 2005 when he published his history of Europe after 1945, “Postwar,” the book that sealed his reputation worldwide. Three years later he was diagnosed with motor neuron disease. Two years after that, he was gone. Which means that his last book, “Thinking the Twentieth Century,” was written — dictated, actually — in bed as he was dying. This critical survey of 20th-century thought is a towering achievement

The first section of each chapter is given over to Judt’s own past: his parents’ meeting in wartime London; the family’s nonstop talk about the Holocaust; reading history at King’s College, Cambridge, where he was awarded an exhibition the year before he was due to take his A-levels (pre-university entrance exams). After the success of “Postwar” he had planned to write a history of 20th-century intellectual life, a plan put paid to by his illness. And then Timothy Snyder, a historian of eastern Europe a couple of decades his junior, proposed they do the book together as an extended dialogue in which they would mull over the mechanics of modern thought. The result is a masterpiece that ranges from Matthew Arnold to Stefan Zweig by way of Friedrich Hayek, Eric Hobsbawm and (the book’s real hero) John Maynard Keynes and will humble anyone who thinks themselves even remotely cultivated.

How, you keep asking yourself, could one man remember all this narrative detail, these abstruse references, these verbatim quotations?

Not that Snyder is a slouch on the memory front. There are times when he caps a triumphant Judt recital with one of his own. But he has nothing to match Judt’s mordant apercus and aphorisms. Thus the Bloomsbury set evinced “the very English idea that aesthetic preferences are foundational for political and (especially) moral views.” Thus Karl Marx was “both an exemplary French political pamphleteer and a minor commentator on classical British economics.” Thus “the time has … come to distinguish between Israel and the Holocaust, since the latter should not be allowed to serve as a get-out-of-jail-free card for a rogue state.”

Phrases like these crop up on nearly every page of this valiant book. Read it and weep that there shall be no more.