Tony Blair regrets, according to one newspaper columnist yesterday, that he chose to read law rather than history at university. The row over whether or not weapons of mass destruction exist in Iraq, however, illustrates that he would have found philosophy most useful.

Last week this newspaper revealed the sort of questions that an applicant for that subject at Oxford has to deal with. Imagine how much easier the Prime Minister would have found life if he had been trained to cope with inquiries such as “How do you define time?”,“How do you know if two plus two equals four in the past?” or “Is it possible to split a human brain in two and create two identical people?” (Correct answer: “I’m not sure but willing to experiment on Clare Short.”)

There is, though, a question regularly asked at an Oxford college which encapsulates Mr Blair’s present dilemma over Iraq perfectly. The applicant is invited into the interviewing room and seated in front of a rectangular coffee table. He or she is asked “how many legs has this table got?” The student can only see three legs from where he is sitting but replies “four”. “How do you know”, the don says, “that there are four legs when you can just see three?” The poor student squirms and attempts to explain how sensory perception can be misleading and that it is possible to reach judgments in the absence of observable data. At the end of the discussion the teenager is invited to stand up and look once more from a different angle. He discovers that the table, despite its shape, has but three legs.

This appears to be the essence of the weapons of mass destruction controversy. Mr Blair, like the Oxford candidate, has made a reasonable case, on the basis of what can be seen and assumed, that there is a biological and chemical arsenal hidden away in Iraq. His tormentors respond with “but where is it?” And it is possible that, as Donald Rumsfeld has inconveniently observed, like the fourth leg it is not there.

Philosophy also reveals that two apparently competing arguments can both be true but flawed. The Prime Minister would again have found this helpful. One side in this controversy insists that “finding weapons of mass destruction is fundamental to Tony Blair’s credibility”. The other camp contends that “uncovering such weapons is irrelevant because Iraq is massively the better for the invasion”. Each assertion is valid but incomplete.

Mr Blair placed enormous weight on Saddam Hussein’s WMD threat before the conflict started, but his record elsewhere (Kosovo, Afghanistan, and especially Sierra Leone) shows that he is happy to intervene abroad for purely humanitarian reasons. His concept of foreign policy is roughly akin to liberation theology. On the other hand, the fact that Iraq has been cleansed of torture chambers is a wonderful thing. Presumably it would be equally worthwhile to dispose of such horrors in other countries too, but achieving consent to do so will now be more difficult if voters decide that they were deceived over why there was such a compelling necessity to topple the Iraqi dictator.

The truth is that while the issue of what material Iraq possessed is not irrelevant, the argument raging at the moment is. It will never be settled to universal satisfaction. If Mr Blair publishes, as he promised this weekend, a new dossier with fresh evidence of WMD, or if the American authorities take television cameras down to film a lake beneath Baghdad filled with anthrax, will it be believed by everybody? No chance. It will be claimed either that the poisons have been planted by the CIA, that they date back to the Iran-Iraq war, or that while some weapons have been found, the quantity is too small to have warranted military action.

Here, the study of history might have helped the Prime Minister. The Iraq campaign could be compared with the Trojan Wars. Was Helen’s face actually that impressive? Or was she merely a decent-looking leggy blonde, similar, perhaps, to Rod Stewart’s current girlfriend (and all the previous ones), for whom one might have sent out the odd boat or two but not a thousand ships? We will, alas, never know.

What is interesting about the whole WMD saga is the different way in which varying parts of the pro-war coalition have reacted to it. Some of the belligerents have been so horrified about the failure to find evidence that they have recanted their previous support; others have changed tack and adopted mass graves located as a surrogate for mass destruction unlocated; some are still (like me) sticking with their original position and fiddling with their thumbs while waiting for the barrels full of bubonic plague to emerge. There are plenty of people who do not care; victory, to them, is all that matters.

What this indicates is that while the anti-war lobby may have looked a diverse and rum lot (stretching from pop stars such as Miss Dynamite to Charles Kennedy — Mr Not Dynamite — to Matthew Parris), the pro-war faction was no less anarchic in its composition.

It included neo-conservatives committed to the promotion of American values everywhere, liberal internationalists devoted to universal principles of human rights, anti-proliferationists who focused on WMD, new-orderists who believe the world was fundamentally changed by the attacks on September 11, old-score opportunists who thought Saddam should have been brought down in 1991 and wanted a second bite at the cherry, and restraining influence types who were none too sure that the war was a fabulous idea but wanted to be involved to stop the United States running riot.

From all this, the philosopher might reach the following conclusion. Not only will it never be agreed whether the conflict in Iraq was legitimate but, regardless, the chances of assembling such a coalition to repeat the exercise elsewhere are minimal.

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