It could have been the open-neck denim shirt or the loose jacket, or perhaps it was the ready smile that gave the impression of something other than a judge. Only the sombre black shoes and socks indicated a cursory bow towards the legal profession. "He looks more like an academic," someone mused, watching him sign copies of his book during Dublin Writers Festival.

In fact, Bernhard Schlink is many things in as many places: in Bonn a distinguished judge of European constitutional law, at Humboldt University in Berlin a professor of law.

He is also the author of The Reader, a highly successful and much-praised novel described by Christopher Hope as "a thriller, a love story and a deeply moving examination of a German conscience".

Schlink was born in Bielefeld, in 1944, and raised in Heidelberg, where his father held the chair of theology. When it came to a career, the young Schlink opted to study literature, language and logic, a combination that eventually nudged him towards law.

But there was a gap in his researches: all legal writings in Germany between 1933 and 1945 were locked away where nobody could get at them, a prohibition especially unacceptable to law students curious to know about the missing war years.

During those years, Schlink's father lost his chair, was demoted and got work wherever he could, as did Schlink's godmother - also a teacher - who refused to follow the curriculum of the Third Reich. Like other awkward-minded teachers, they were moved about, passed over, ignored in the pecking order.

"They survived, " says Schlink . "It wasn't a matter of life and death for them." But the past was always present, something he had to deal with. "One of my teachers at the gymnasium had an SS tattoo on his arm, showing his blood group and his SS identity number. The same sort of mark that Jews from the concentration camps had, as a matter of fact."

In 1961, when Schlink was 17, Adolf Eichmann was tried received wide coverage in Germany. "And so did the Nuremberg trials," he says. "They were the formative influences on our adolescence. After that came the awkward questions about the war, and then the student unrest."

Meanwhile, his own life followed its course. He married, divorced, was appointed a judge, helped draft the constitutions of two emergent European democracies and started to write.

In 1997, The Reader, published in Carol Brown Janeway's excellent English translation, was awarded numerous European literary prizes, translated into 31 languages and reached the top of the New York Times best-seller list.

It's not a difficult read: 216 pages set out in short chapters, using a simple sentence structure and a vocabulary that is in no way challenging. What are challenging, however, are the plot and the philosophical questions it raises.

A 15-year-old boy has an affair with a woman of 36. When she mysteriously disappears, the boy is bereft but goes on to study law, next encountering his former lover when he attends a war-crimes trial and finds her in the dock.

Unknown to him, the woman he had loved and not been able to forget had, during the war, been a Nazi prison-camp warder. The story is, of course, a metaphor for post-war Germany, its troubled children and the people who begot them.

But the character of the boy is so well drawn and the eroticism so delicately handled that one has to ask how autobiographical the book is. "That's not a question you can ask," he protests, giving a pleasingly illogical response to a question that had indeed been asked.

He shakes his head. "No, it's private. In any case, this is a novel. It says so." And, picking up a copy of the book, he searches its covers, frontispiece and blurb in vain for the word "novel". Returning the book to the table, he gives his enigmatic smile. "People will have to make up their own minds."

And what of the boy's words - "I was afraid: of touching, of kissing, afraid I wouldn't please her or satisfy her." Is satisfying his partner a priority for a 15-year-old? "There are 15-year-olds and 15-year-olds," Schlink says, smiling again, leaving the comment hanging for the reader to deal with.

There are other questions that confront the reader. Is the sublime happiness of past times destroyed by a subsequent knowledge of duplicity? How far, if at all, must the betrayed person go in showing compassion? What if the loved one is found to have committed the worst crime of the 20th century? Should they be helped in their rehabilitation, and how hard does one try to understand their motives? If your loved one turns out to be a Nazi, can you still love the singer, though not the song?

The boy who is now a man wrestles with his memories but comes up with few answers. What emerges is Schlink's belief in the power of the word. In a denouement that is not totally convincing, the woman is revealed to be illiterate, and the man hangs on to this, believing it to lie at the core of his lover's character. If only she had known how to read she might have got a better job, might not have gone to work in a Nazi prison camp.

"We need institutions," says Schlink. "The church, a political party, a trade union, the family. But when all these have broken down, the only one left is literature. It is part of our morality. In prison, people console themselves with poetry." In Schlink's novel, the woman's illiteracy represents society's moral breakdown.

During a recent sabbatical in New York, he shared a platform with Daniel Jonah Goldhagen, whose book, Hitler's Willing Executioners, points the finger not only at the Nazis but at the German people as a whole. Did Schlink find this racist? "No, I didn't find Goldhagen racist, simply wrong. There was something so universally frightening about the Third Reich that he had to confine it to a specific group."

So why did the Holocaust happen in Germany and not replicate itself as a pogrom against black people in America where, at the time, conditions were broadly similar? "Because there they have never been as prone to ideologies as Europeans have. Americans are mobile. They do it, then they drop it: Catholicism, Buddhism, the marines. I admire them for that."

He shows polite interest in a news report of a Jewish group that is suing the French railways for their part in transporting people to the death camps, but wonders where you draw the line. "What of the RAF, which dropped all those bombs on Dresden in the final months of the war? Are they to be sued?"

And what of the Palestinians, made to pay the price for a war not of their making, I ask. Is there a line to be drawn there? We discuss the Arabs who lament the harshness of their history, and of their Jewish neighbours, who do the same.

"Yes, and" - lowering his voice - "they still do. Of course history isn't fair, but you can't go on for ever being bound to old wounds."

The Reader is published by Phoenix Press (£6.99 in UK)

Bernhard Schlink's visit to Dublin Writers Festival was part of the Arts Council's Critical Voices programme, in partnership with The Irish Times and Lyric FM. The programme is bringing international writers, critics and artists to observe the cultural scene here and to participate in public debate over the next six months. Further information from www.artscouncil.ie