And when some professors at a City College teach- in claimed that American foreign policy was responsible for the attacks, Matthew Goldstein, chancellor of the City University, denounced "those who seek to justify or make lame excuses" with arguments "based on ideological or historical circumstances."

Still, Dr. Goldstein and Ms. Cheney would surely agree that scholars should explore the ideological or historical context of the attacks. That is what we want our professors and teachers to do, especially in the heat of crisis. Not all scholars will be careful in their analyses, and some may be downright stupid. But that's the price paid for open debate.

If Dr. Goldstein's reaction, and that of Ms. Cheney, are interpreted (perhaps wrongly) as discouraging inquiry into the attackers' motivation, they will be of no help to our security, which ultimately depends on understanding terrorism's causes so we can know how to reduce its likelihood. Teachers and those who monitor them need to distinguish between excusing horrific acts and explaining them. That is not always easy, but we manage it in other contexts.

For example, history teachers explain that mistakes of America and its allies contributed to Nazism's rise after World War I, when the victorious powers insisted on reparations so onerous that Germany was left in ruins.

"American History" by Donald A. Ritchie, a textbook used by many eighth graders nationwide, says that "heavy war debts and rising unemployment caused great discontent among the German people and led directly to the rapid growth of two antidemocratic parties - the Communist Party and the Nazi Party."

Nobody thinks such explanations excuse or justify Nazism. Indeed, analyses of earlier policy mistakes shaped American actions after World War II: the Marshall Plan for European economic recovery was intended to avoid repeating errors that contributed to, but did not excuse, Hitler's rise.

Teachers distinguish explanation from excuse in addressing domestic policy as well. In studying urban race riots of the 1960's, children learn that police brutality, unemployment and discrimination created conditions from which violence erupted. The "American History" text recalls that President Lyndon B. Johnson commissioned a report on urban violence that "laid responsibility for the ghettos at the feet of white society."

Having given that explanation, no teacher should be accused of suggesting that rioting ought to be tolerated or perpetrators left unpunished.

Young people have to learn to distinguish explanation from excuse in criminal justice policy, too. Experts know that victims of child abuse, for example, are more likely to abuse their own children. For most Americans, this implies not that child abusers should be treated with leniency, only that addressing the causes of abuse is needed to prevent it.

In the case of Hitler, or Osama bin Laden, the line between explaining and excusing should be apparent to all. So the last thing we should want is to inhibit professors and teachers from exploring Islamic fundamentalism, the Arab-Israeli conflict, the politics of oil, the role of authoritarianism in the Persian Gulf region, how American mass culture is marketed internationally or anything else that might help to understand and prevent recurring terrorism.

Ms. Cheney may be right in suggesting that there is no sense in which terrorism is "our fault." Perhaps there are no policies the nation has followed that we would want, upon reflection, to change. If, as some have said, the attackers reacted only to our culture and freedoms, then policy makers can get little help from academic inquiry into the motivation. But teachers should be encouraged to explore whether there are specific policies that may give rise to terrorism, without being accused of undermining patriotism and national unity. Students who are not taught to question our polices will be ill prepared as adults to improve on them.

In Britain, Prime Minister Tony Blair had a campaign slogan: "Tough on crime. Tough on the causes of crime." He meant that his government would be as determined to correct the social policy failures that contribute to crime as it would be to punish offenders.

That is a good model for discussing terrorism. The government should be tough on terrorism, but professors should explore how we can be equally tough on its causes. If they don't, it is unlikely that others will.

E-mail: rrothstein@nytimes.com.