"Never," I said, not waiting to be called on. This was easy. "Constitutional rights are absolute."

"That's not a very sophisticated view." She looked at her seating-plan. "Marcus. For example, say a policeman conducts an improper search -- he goes beyond the stuff specified in his warrant. He discovers compelling evidence that a bad guy killed your father. It's the only evidence that exists. Should the bad guy go free?"

I knew the answer to this, but I couldn't really explain it. "Yes," I said, finally. "But the police shouldn't conduct improper searches --"

"Wrong," she said. "The proper response to police misconduct is disciplinary action against the police, not punishing all of society for one cop's mistake." She wrote "Criminal guilt" under point one on the board.

"Other ways in which the Bill of Rights can be superseded?"

Charles put his hand up. "Shouting fire in a crowded theater?"

"Very good --" she consulted the seating plan -- "Charles. There are many instances in which the First Amendment is not absolute. Let's list some more of those."

Charles put his hand up again. "Endangering a law enforcement officer."

"Yes, disclosing the identity of an undercover policeman or intelligence officer. Very good." She wrote it down. "Others?"

"National security," Charles said, not waiting for her to call on him again. "Libel. Obscenity. Corruption of minors. Child porn. Bomb-making recipes." Mrs Andersen wrote these down fast, but stopped at child porn. "Child porn is just a form of obscenity."