Those who argue against an invasion of Iraq do so with a blend of naivet? and cynicism.

It's all about oil, they say. War with Iraq will simply cause more terrorism, they say. Containment is working. We can win without war. Bush wants to start an American empire. These pronouncements are often delivered with some force, as if to suggest that demurral could come only from some brutish and ethically-challenged person, probably adrift in the same world of macho fantasy inhabited by the staff of the Bush White House.

All of these arguments against invasion assume that the stated American position on Iraq is untruthful. None of them holds enough water to drown an unusually small fruit fly in, but - to borrow a few well-chosen words from the American columnist Victor David Hansen - it is "neater to create rather than recall facts, and better to feel good about oneself by adopting platitudes of eternal peace and universal tolerance than to talk honestly of evil, war, and the tragic nature of man".

The truth of the matter is that no one knows whether war with Iraq is the right course of action or not, not because all war is wrong, but because there is no precedent for the dilemma we are now facing. The events of the last few months and years have been such a profound departure from the normally accepted rules of the game of international relations, that all that is plain and obvious is that those events require a response. Doing nothing would be absurd in the circumstances.

We have now come to one of those moments in world history when we have no prior experience to guide and inform us. It is a moment that is going to require the West to make a leap of faith.

But let's get rid of the rose-tinted glasses for a moment. It's a leap that must be taken against this backdrop: The tragic nature of man being what it is, violence and war are as much a part of our lives now as they ever have been. Perhaps there is reason to hope that it will be otherwise one day. Perhaps not. In the meantime, we cannot wish war away or cut ourselves off from the possibility that we may need to use it to defend ourselves. The qualities that are needed in those who will guide us in our leap are clarity of mind and courage, not wishful thinking and timidity.

Lee Harris, a writer for Policy Review and a contributing editor for the think tank called Tech Central Station, uses the analogy of a game of chess to describe the position the West is in. Two equally skilled players, no matter how bitter the conflict between them, understand each other's rationale and motivations, and will play the game according to its rules until one or the other emerges as the victor.

"But what happens," he asks, "when you are playing chess with someone who refuses to accept the rules of the game? How do you respond if your opponent begins to jump his knight in all sorts of bizarre zigzag patterns, so that you cannot predict where he will land or what piece he will seize?"

In chess, of course, the answer to this dilemma is to stop playing with the madman sitting at the board with you and find another, worthier opponent.

In the conflicts we now find ourselves in that involve al Qaeda, radical Islam, Palestinian extremists, Saddam Hussein in Iraq, and others, there is no such choice.

Our opponents are not playing by the rules that have governed international conflict in the past. We are facing opponents who do not behave "rationally", and who therefore cannot be dealt with "rationally".

Says Mr.Harris: "That precisely is the nature of the crisis we are facing. The world system has collapsed internally: there is no longer a set of rules that governs all the players. And here I do not mean ethical rules, for that cannot be expected, but what Kant called maxims of prudence, those regulatory principles that enforce a realistic code of conduct on all the participants in a well-ordered system, and which allow us to know for a near certainty what the other players will not even conceive of doing.

"This collapse of the well-ordered system has come about exclusively from the side of the Islamic world. No other party has contributed to it. And the cause of this disruption is the lack of a sense of the realistic on the part of certain elements in the Islamic world. This is not a cultural judgment, but a fact - at least as much a fact as any such judgment can ever be. "

Those who are looking for a common thread that unites Iraq, al Qaeda, and Palestinian terrorism, he says, will find it in a mindset that can conceive of flying airplanes into buildings, not as a method of gaining some advantage, but as an end in itself.

The West's dilemma is given the most dangerous dimension possible by the potential of nuclear and other weapons of mass destruction. By actions or by words, all three of these entities have demonstrated that they wish to acquire nuclear weapons. Iraq has already used non-nuclear weapons of mass destruction against its own people and against Iranian troops.

Before 9/11, it might have been correct to react to the suggestion that these weapons have been, or might be acquired by these groups by asking, "Yes, but is it reasonable to expect them to use them against us?" Since 9/11, the question has changed. Now, it is "Which will be the first to use them?"

The only way out of this dilemma, writes Mr. Harris, "is to make the Islamic fantasists respect the dictates of reality. If they wish to compete with us, if they wish even to be our enemies, we will accept that, as we accepted this situation with the Soviet Union during the Cold War. But they must be made to accept the basic rules of play - rules that are accepted by the rest of mankind, from the US to Communist China.

"And that is why, in order to achieve our end of heightening their grasp on reality, no means should be ruled out. We must be prepared to use force 'unstintingly', as Woodrow Wilson declared on America's reluctant entry into the First World War. On this count, we must have no illusions. Until they are willing to play by our rules, we must be prepared to play by theirs.

"If we are to teach others a sense of the realistic, it is imperative that we not lose our own. We must not let our noble ideas betray us into betraying our very ideals. The only way that these ideals will find a place in the world of tomorrow is if we are prepared to defend them today - and to defend them at whatever cost is required."

This is what drives the Bush White House, and it is what makes Prime Minister Blair and some other European leaders so clear about the necessity to make common cause with the United States. Months ago, it was airliners flown into skyscrapers. Months from now, it might be a city turned into a nuclear fireball for not much better a reason than an opportunity to watch how it humbles the mighty.

This new world reality, some say, demands a new type of world order.

Writing in , Paul Johnson, a British historian and author (most recently of the biography, ), argues in his article, , that the United States must take the lead, and act as a world policeman.

"Imagine a world," he said, "in which the United States was stricken by a successful series of nuclear, biological, and chemical attacks. Putting aside the appalling loss of American lives this would involve, the global consequences would be horrifying. The world would be plunged into the deepest depression in its history. There would be no power-of-last-resort to uphold international order. Wolf and jackal states would quickly emerge to prey on their neighbours. It would be a world as described by Thomas Hobbes in his (1651), in which, deprived of a giant authority figure 'to keep them all in awe', civilisation would break down, and life, for most of mankind, would be 'nasty, brutish and short'.

"Hence, we do well to look at the crisis not as solely or even primarily an American problem, but as a global one. We need a Leviathan figure now much more than in the 17th Century, when the range of a cannon was a maximum of two miles and its throw-weight was measured in pounds. America is the only constitutional Leviathan we have, which is precisely why the terrorists are striving to do him mortal injury, and the opponents of order throughout the world - in the media, on the campus, and among the flat-earthers - are so noisily opposed to Leviathan's protecting himself.

"But Leviathan will not be deterred. He is in arms, and knows what he has to do. Moreover, he is not a solitary autocrat as in Hobbes's day, but a constitutional ruler with an educated people of nearly 300 million behind him.

"To vary the metaphor, the clock is ticking towards high noon but the sheriff is buckling on his belt and the citizens are aroused. Mr. Bush has been given a mission by the brutal logic of events and he must carry it out promptly and in full. Is America, then, a world policeman? The answer must be: Yes, and thank God for it! Progress has contracted all distances and made destructive forces almost limitless. So the world is now too small, and the weapons of the malefactors too devastating, for us to do without a constabulary enjoying full powers and global reach. As Mr. Gladstone once said, 'the resources of civilisation are not yet exhausted,' and Mr. Bush has no moral alternative but to put himself at the head of them, and point the 21st Century in the direction of world order and peace."