"Dr. Dennehy and I are serious people who respect each other and have become friends over the years," Potts told the class as it met last fall. "We don't abuse each other. We don't try to spin data or philosophical interpretations in unreasonable ways."
Dennehy, 75, is a dapper professor of philosophy, bioethics and epistemology at the University of San Francisco.
He argues that abortion is almost certainly the killing of an innocent human being and that the Supreme Court's 1973 Roe vs. Wade decision, which has led to about 1.3 million legal abortions a year, "has had the effect on democracy that an atomic bomb would have on any city."
Potts, also 75, is a rumpled, British-born embryologist and gynecologist who has worked to make the procedure available to women in developing countries.
He contends that it is scientifically impossible to determine when life begins, but concedes that "I would rather destroy a five-week embryo than a 15-week embryo, and I accept there is some stage in pregnancy that you have to say no."
It's amazing how many of these students need a class in basic logic.
Have you ever been raped or been pregnant?" a young woman demanded.
You could almost see Dennehy rolling his eyes.
"Suppose I said yes," he said, unable to keep a slight snippiness out of his voice. "What's your next move?"
"I was just curious how your opinion would have changed if you were in that situation."
"What has that got to do with the validity of my argument?"
Her gambit failed; now she was on the defensive: "It's just a question."
"There are only two issues in an argument, miss," Dennehy said. "The facts, and the conclusions you draw from the facts.
"When we teach logic, that common fallacy is one of the first things we teach: shifting the attention of the argument and the evidence to the person arguing. It's absolutely irrelevant."