When it came to Hitler, Karl Kraus, the Viennese satirist, said that he couldn’t think of anything to say. This sounds odd, first because Hitler was, and will remain, an inexhaustible subject for biographical and psychological speculation, probably beating Napoleon or Stalin in the amount already written about him; and second because Kraus wrote millions of words and had an opinion about almost everything else. But one knows what Kraus meant. “Whereof one cannot speak, thereof one must be silent,” wrote another Viennese, the philosopher Ludwig Wittgenstein, albeit in another context. The unspeakable is the largest subject of all. I remember one of the first prisoners I met as a prison doctor. He had killed three children and then impaled them. Of course, it is not the place of a doctor to expatiate on the sins of his patients: the man had bronchitis and needed treatment, that was all. But …