Christian thinking on violence and war ranges from total pacifism to the just war theory. The term "just war" is a misnomer, since war itself is never good. The just war theory is really a theory of permissible participation in war by (at most) one side, and it is in that sense that the term is used in what follows.

To count as just, a war must be fought in self-defence or in defence of others unjustly attacked; and since there are other criteria to be met, not all wars of self-defence necessarily count as just.

How can a Christian, with the words of Jesus about turning the other cheek in mind, possibly think that waging war could ever be justified? A Christian has a right to self-defence, and so may resort to force when all else fails. However, it is permissible for him/her to waive that right and allow him/herself to be killed rather than use force.

But when it comes to defending others in one's care, the Christian may not waive the right to self-defence. The mother who defends her child against lethal attack by an aggressor, even if it leads to the aggressor's death, acts rightly - indeed, it would be morally wrong not to do so.

The Christian must be concerned about both peace and justice. Similarly, two fundamental moral principles apply to the state. It must (a) keep the peace and avoid war, and (b) stand up for justice within the limits of what is possible, i.e., when it comes to defending other countries or oppressed peoples against attack. The purpose of just war theory is to balance these two principles. Interpreting its criteria too strictly betrays (b), while taking them too loosely undermines (a).

At the time of the Gulf War many western critics of the US-led offensive either interpreted the just war theory too strictly, or rejected the theory as out of date because it did not indicate that President Bush was wrong to authorise the offensive. A few years later many of the same people were all in favour of NATO bombing the Serbs, regardless of its effectiveness, thereby erring on the side of laxity.

The just war theory has two parts. First, the criteria with respect to choosing war:

1: just cause (defence of one's own or other countries against unprovoked actual or imminent attack);

2: competent authority (usually, only a government has the right to declare war);

3: comparative justice (since there is often fault on both sides, preponderance of fault must lie on the other side);

4: right intention (roughly peace with some justice);

5: last resort (all other non-violent means having been tried);

6: reasonable prospect of success;

7: proportionality (the good to be achieved by going to war must not be outweighed by the harm war causes)

Second, the criteria with respect to the conduct of war: (1) proportionality (as above); and (2) discrimination (non-combatants must not be indiscriminately targeted.)

These are strict criteria and quite often they are difficult to fulfil. Of course the just war theory is open to misuse, but so are all moral theories. Misuse is no excuse for rejecting it, however. In practice the real target of the just war theory is not pacifism, but those who too lightly proclaim the rightness of taking up arms.

For example, the 1916 insurrection and the recent IRA campaign fail virtually all the criteria. Given the passing of the 1914 Home Rule Bill and the way Canada and Australia became independent, the 1919-21 War of Independence seems to have been neither necessary as a last resort nor was it proportionate.

On the other hand, Ireland's policy of military neutrality is in trouble on two counts. First, it means refusing to accept the obligation to defend others - our failure to support the UN offensive against Iraq in January 1991 was not moral. Secondly, it involves the intention to defend ourselves by force, alone, against attack - an intention to fight a war we probably cannot win and which violates the "just war" criterion of reasonable prospect of success.

Where the proposed Anglo-American military action against Iraq is concerned a number of points can be made:

1: aerial bombing (as in the second World War) targeted at civilian population centres - as with the use of landmines and chemical or biological weapons - fails the discrimination criterion and hence is immoral. Despite technical improvements, it is still doubtful whether precision bombing of military targets in population centres can pass the discrimination test.

2: sanctions are indiscriminate, and the nature of the Iraqi regime is such that they affect civilians far more than soldiers. Their ineffectiveness means that the population's suffering is pointless, and so they violate the proportionality criterion. There is a strong case then for abandoning them. This point also offers further vindication of the January 1991 offensive, as sanctions alone would never have got Iraq out of Kuwait.

3: attaining military objectives usually requires ground forces. The apparent intention to use air power alone, which punishes but does not defeat, reflects an absence of clear and attainable military objectives. It follows that the prospect of success and proportionality conditions are not being met.

4: ridding Iraq of weapons of mass destruction is morally laudable. Unfortunately, we do not have an international legal order, backed by force, and overriding national sovereignty. It is not yet accepted that the UN should be able to take military action against states developing certain kinds of weapons or treating their peoples genocidally, as it is accepted in the case of attack by one state or another. The UN does not then constitute a competent authority in the relevant sense. Finally, since Iraq is not at present threatening to use its weapons on its neighbours, the just cause criterion is not fulfilled either.

Apart from their moral significance, application of the just war criteria leads to a conclusion curiously parallel to the doctrine of the war theorist Clausewitz - that the use of military power in a way that ignores political realities may render military victory hollow and even lead to political defeat - as happened to the US in Vietnam. It is to be hoped that air strikes against Iraq will not ultimately yield Saddam Hussein a political victory, since it matters very much to all of us that Mr Saddam does not win and that the US is not driven by political defeat into isolationism.

Father Seamus Murphy SJ teaches philosophy at the Milltown Institute of Theology and Philosophy in Dublin