Every new generation changes the rule-book - sometimes it's a tweak, sometimes it's a wrench from the past. Even my own mother was considered somewhat unchaste by her parents for talking about boyfriends with my sister and me .The gramps would be turning in their graves if they knew about some of the fruitier chats I've had with my own daughter on the same subject.
How was it possible that during the 20th century people from Germany, a cultured nation at the heart of Europe, perpetrated such crimes? In my attempt to answer this, I was helped by two accidents of history. The first was I met many former Nazis at exactly the moment when most had nothing to lose by speaking openly.
There can't be too many Jewish reviewers as acquainted as I am with the 13th-century Franciscan friars who people David Flusfeder's book. You were perhaps studying Torah at Limmud while I notionally embarked on a medieval road trip (from Oxford to Viterbo) with John the Pupil, his two pilgrim sidekicks and a precious package for the Pope.
A few weeks after Adolf Hitler was appointed Chancellor of Germany by President Hindenburg in January 1933, the first Nazi concentration camp was set up in a derelict munitions factory at Dachau, just north of Munich. On March 22, the first detainees arrived.
It was a scorching hot June afternoon in a Baghdad suburb. A group of people sat in the shady garden, speaking rapidly in Arabic, catching up on almost two decades of gossip. It was 2003, just months after the invasion and I was staying in the upmarket district of al Mansour with one of the Iraqi opposition leaders.
When Adolf Eichmann stepped into the bullet-proof glass booth specially designed for his trial in Jerusalem on 11 April 1961, there was a universal sense of anti-climax. Was this soberly dressed, bespectacled and balding middle-aged man the same figure whose name terrified Jews in the Third Reich?
'T he man possesses the genius of looking at life face to face, of thinking not in concepts but in the fundamental facts of reality". So wrote Ben-Gurion about Lenin, whom he further described as "a man of iron will who will spare neither human life nor the blood of innocent babes for the sake of the revolution".