The Sept. 11 attacks in the U.S. that year appalled Mr. Kalisch but didn't dent his devotion. Indeed, after he arrived at Münster University in 2004, he struck some as too conservative. Sami Alrabaa, a scholar at a nearby college, recalls attending a lecture by Prof. Kalisch and being upset by his doctrinaire defense of Islamic law, known as Sharia.
In private, he was moving in a different direction. He devoured works questioning the existence of Abraham, Moses and Jesus. Then "I said to myself: You've dealt with Christianity and Judaism but what about your own religion? Can you take it for granted that Muhammad existed?"
The professor says he's more determined than ever to keep probing his faith. He is finishing a book to explain his thoughts. It's in English instead of German because he wants to make a bigger impact. "I'm convinced that what I'm doing is necessary. There must be a free discussion of Islam," he says.