The resort to violence is never uncontentious, as ongoing controversies over the 1916 Rising and possible military action against Iran's nuclear programme attest. Helpful in clarifying both cases is the centuries-old just war tradition. Though in all its intricacies it can fill tomes and includes multiple criteria, its essence can be boiled down to two tests: is the use of violence proportionate to the injustice suffered or threatened; and have all other options been exhausted.
Consider first Iran's nuclear ambitions. By just war's two central tests - proportionality and last resort - how does the case for forcibly halting its nuclear programme measure up? The first test requires an evaluation of the extent to which the theocratic state's acquisition of nuclear weapons would increase the prospect of millions of innocent lives being lost in a nuclear holocaust. The risks come less from its often belligerent leadership deploying such weapons - the knowledge that retaliation in kind could in minutes obliterate 5,000 years of Persian civilisation is almost certainly deterrent enough - but from two other sources.
First, the UN's nuclear non-proliferation treaty (NPT), which Ireland played a central role in drafting, and which remains the country's greatest contribution to global security, is fraying. North Korea has breached the treaty and built a bomb. Three non-ratifying countries have already gone nuclear. A review of the treaty's functioning failed last year. If Iran crosses the line the treaty will be a dead letter. The result would be rapid proliferation, centred on the Middle East, a tinderbox region where multiple nuclear hair-triggers could cause a cataclysm.
Even more serious is the risk of "loose nukes". The regime is divided, unstable and domestically unpopular. The risk of nuclear know-how, material, and/or ready-to-deploy bombs making their way into the hands of terrorists via the regime's extreme or rogue elements is considerable. That risk would multiply if the regime were to collapse - an outcome that is, sooner or later, inevitable. Given the magnitude of this threat, the use of limited military action to destroy Iran's bomb making capacity would, therefore, pass the proportionality test.
It remains, however, a long way from passing the last resort test. A process of sanction is about to begin at the UN Security Council. This will involve a ratcheting up of diplomatic and economic pressure on Iran. To these sticks, carrot will also have to be added. Realpolitic dictates a recognition of Iran's security interests as legitimate, no matter how illegitimate its illiberal and anti-democratic regime. Because the US is the dominant power in the region, it is the only country that can give Iran the security guarantees that might possibly persuade it to step back from the brink. Reluctant though the US is to offer such guarantees, for reasons both good and bad, it will have to do so if military strikes against Iran's nuclear facilities are ever to be justified. And while the matter has inevitably become linked to the conflagration in Iraq (the invasion of which, incidentally, emphatically failed just war tests), its gravity means that the case will ultimately be treated on its own merits.
If the possible resort to military action in the Middle East will top concerns for the international community in the near future, the consequences of the use of force in the past continue to have repercussions in Ireland. Again, just war thought helps clarify the issues.
First, was resort to violence a proportionate response to the injustices associated with British rule in the early 20th century? Though historians differ on many issues relating to the period, none maintains that there was anything more than minuscule support for a violent response in 1916. This strongly suggests that most people at the time did not believe that the injustices they endured warranted a violent response. (It is often said the subsequent and rapid change in public opinion vindicated the decision to stage the rising, but the just war tradition excludes retrospective justification as this could allow anyone to use violence and claim the future will vindicate them.)
If the rising did not pass the proportionality test, it failed the last resort test by an even wider margin. Those involved had made little effort to convince public opinion that their vision trumped the devolution on offer at the time, even though the many non-violent tactics deployed by their contemporaries - from trade unions to the Suffragettes - were untried. It is unsurprising, therefore, that the organisation most closely involved in refining the just war doctrine over the centuries - the Catholic Church - was among the sternest critics of the 1916 Rising. Numerous bishops condemned the action, and their thinking was informed by the just war tradition.
States around the world born of violence do not apply just war tests to their origins.Such states are also secure in the knowledge that the ghosts of their revolutionary founders are safely at rest in national pantheons. But because Ireland's revolutionary ghosts have been uniquely active, the issue has remained live. And if President McAleese's Cork speech and the reaction it elicited are anything to go by, it is a long way from conclusion.
Dan O'Brien works at the Economist Intelligence Unit.