We must not allow our desire for revenge lower our moral standards

September 11: that's all you need to say, and everyone knows immediately what you mean.

No other catastrophic event in world history is labelled simply by a date - we may know exactly what we were doing when Kennedy was assassinated, when Kurt Cobain killed himself or when that airliner blew up over Lockerbie but very few people could identify the events by a simple mention of the dates.

This is yet another way in which the terrorist attacks on New York and Washington have changed the world.

Perhaps it's not the world itself that has changed - there have been mindless atrocities before, some of them on a scale as large as this - but our way of looking at it.

Helpless in the face of incomprehensible evil, we sense that the old moral certainties of the Western world can provide us with no answers.

Love will not find a way, turning the other cheek brings no respite, even giving in and surrendering makes no sense, because these terrorists make no demands, and it seems there is no way of appeasing them.

They are the joyful martyrs, we are merely their victims, and all they want is to destroy/punish/frighten us, and so our ethical system cannot provide us with an adequate way of responding.

As Jeremy Irons said in that brilliant but depressing film The Mission, "If might is right, then love has no place in the world".

No wonder that even ardent pacifists are rethinking their positions, and that the issue of capital punishment is raising its ugly head again. When there is no way of arguing with your oppressor, for many people the only way of responding is to lash out in blind hatred, no matter how futile that may be.

But we have to be careful. A demand for the death penalty for Amrozi very easily can extend to a hatred for all people who look like, worship in the same way as, live in the same country as him.

It's easy to fall into the David Oldfield trap and assume simply that because most terrorists are Muslims, most Muslims must, therefore, be terrorists - it may be a fundamental error in logic, but there's something comforting about it.

Absolute terror, absolute evil (and those are the terms in which we in the West see the events of the past two years) do demand a new way of thinking about how we deal with them. But it's not the first time that people in the West have had to face this moral issue.

Let me mention another date: July 20, 1944. It probably doesn't ring a bell with many people, but it was the day of the von Stauffenberg plot, sometimes known as the Generals' Plot, to kill Hitler. It failed, and the conspirators were hanged slowly with piano wire (Hitler's favourite entertainment in the following months was to watch the film of the executions over and over again).

Many reasons have been given for this plot: the generals' knowledge that the Germans were going to be defeated, so they attempted to make themselves less culpable; their universal hatred of this working-class upstart Hitler; even a genuine attempt to stop the atrocities against the Jews.

What is more important in the wider context is to realise that among the conspirators was a gentle German pastor and academic, Dietrich Bonhoeffer, a pacifist and teacher of ethics, who gradually came to the realisation that he could no longer stand by and do nothing about the evils of the Nazi regime.

"We have been silent witnesses of evil deeds," he said. "We have learnt the art of equivocation and pretence." And he came to see that the purpose of ethics was not as simple as just doing good but to change the world for the better, which might mean choosing between two evils.

So his involvement in the assassination plot came about gradually, when he was faced with an evil that was outside his normal frame of reference.

Although he couldn't be directly involved, he helped make it possible for others to carry out the attempt for, in the words of theologian Larry Rusmussen, "to want something done, but to refuse to take part in doing it, is a parasitic position".

Bonhoeffer's world was changed by Hitler, forcing him to rethink his former pacifist position, and to realise that pacifism is not necessarily the same as passivity.

The terrorist attacks of September 11 changed our world, and many people in the West are rethinking their attitudes, too.

But, like Bonhoeffer, what we must realise is that taking steps to defend the world against evil is not the same as taking revenge against the perpetrators of evil deeds.

To call for the death penalty for the Bali bombers, say, is to reduce ourselves to their level, as despicable a position as gloating over the bodies of the sons of Saddam Hussein.

Bonhoeffer believed that Hitler had to be exterminated, even if it meant killing other people as well, because it was a lesser evil that would bring about a greater good. But if he had not been executed just before the war ended, I wonder whether he would have called for the death penalty for the perpetrators of the Nazi atrocities at the subsequent Nuremberg trials?

I suspect that revenge never became part of his ethical belief system.