Alive in the closing decades of the Western Roman Empire, St Augustine of Hippo devised a clever answer to one of civilisation’s oldest questions: when is it right to go to war? But unlike most contemporary theories from his era, from whether the sun goes round the earth, to whether slavery is acceptable, Augustine’s ideas on Just War theory are still in currency today.
Although the Christian theologian never wrote a checklist for what constitutes a ‘Just War’, scholars have distilled his disparate thoughts on war into six conditions for a conflict to be considered morally justifiable. The war must be waged by a legitimate authority; fought for a just cause; driven by right intention; a last resort, after diplomatic efforts have been exhausted; proportionate to the harm it seeks to prevent; and it must have a reasonable prospect of success.
Sixteen centuries on, politicians, philosophers and the military still reach for this framework when they want to know whether a war can be justified. St Augustine’s principles have not always been paramount – in 1965, the UN Security Council condemned all forms of armed intervention. But, as Paddy Ashdown noted in 2008, the criteria used to justify military engagement under the duty to protect bore a ‘remarkably close resemblance’ to St Augustine’s six conditions for Just War.
The theologian’s analysis is useful, certainly. The question, though, is whether it still deserves the trust we place in it.
Start with perhaps the most troubling requirement: legitimate authority. Many modern legal experts argue that an explicit authority from the United Nations is required for military action to be lawful. Since Russia and China have vetoes on all declarations from the United Nations Security Council, St Augustine’s conditions confer legitimacy onto the decisions of these authoritarian regimes. It means that humanitarian interventions, such as those to prevent mass slaughters in Kosovo and Libya, which were not fully endorsed by the UN Security Council, are not fully ‘just’ in the eyes of Augustine.
The world of settled states issuing orders through clear chains of command is foreign to many modern conflicts. When a village militia takes up arms because no state will defend it, or when a population under occupation organises its own resistance because its government has collapsed or been captured, the demand for “legitimate authority” risks disqualifying exactly the actors most in need of moral cover. Augustine’s theory struggles to bless the resistance fighter but may favour the invader’s government. Far better to judge whether the people fighting a war are answerable to those they claim to defend.
This leads to a further flaw in St Augustine’s account, which imagines a neat episode of war bookended by a declaration at the start and a surrender or diplomatic deal at the end. More often, the tempo of violence, only some of which is directed by a state, rises and falls, and continues to splutter long after the main political issues have been settled. Any ‘just war’ theory assumes violence can be grouped together and justified collectively. Given that violent crime is almost always judged as a series of individual acts, the concept is clearly missing something.
But there is a real genius in St Augustine’s work, in that it predates developments in moral philosophy by more than a thousand years. His six conditions belong to three different families of ethics. Proportionality and reasonable prospect of success are consequentialist tests — they ask what the war will produce, weighing harm against benefit. Just cause and last resort are best understood as tests of action: was this the right thing to do, given the alternatives available at the time, independent of how it turns out? And right intention is a test of character — it asks not what was done but who was doing it, and why.
Legitimate authority sits somewhere between action and character: it asks who has the standing to act on a community’s behalf. Augustine, without naming Aristotle and certainly without ever knowing any of Kant’s work from more than a millennium later, had already built a theory that borrows from consequentialism, deontology and virtue ethics all at once. That’s not a flaw. It’s why the framework has outlasted the rival approaches which have tried to reduce war to a single moral currency.
None of this means every condition still applies with equal force. Wars can’t be sorted neatly into “just” and “unjust.” And it’s certainly not the case that a war which fails one condition is as bad as conflict which fails all six.
It’s more honest to see justness as a spectrum, with wars ranking higher the more of Augustine’s conditions they satisfy, and how fully. Judged this way, Ukraine’s resistance to Russia’s invasion sits near the top: a defensive cause, an exhausted diplomacy, a proportionate response, and a democratic authority that answers to the people it represents. The Allied fight against Hitler in the 1940s belongs beside it, for much the same reasons, magnified by the scale of what was at stake. Both wars pass every test Augustine set, including the one modern conflict tests hardest: a government fighting because its people asked it to, not the other way round.
Just War theory is still relevant and important. It can apply to modern conflicts. But to apply it properly requires thought and moral imagination, perhaps in the tradition of radical insights set by the visionary work of St Augustine of Hippo sixteen centuries ago.
