In order for a war to be just, three things are necessary. First, the authority of the sovereign. Secondly, a just cause…Thirdly…a rightful intention. ~Thomas Aquinas, Summa Theologica
In the wake of the Russian invasion of Ukraine on February 24, 2022, and growing fears that the ensuing war could escalate and expand in dramatic ways in the coming days and weeks, it is an apt moment for reflection upon the ethics of the use of force, in general, and of waging war,1 in particular. Here, I will articulate some general reflections of my own, as well as provide a very brief primer on the most influential philosophical framework for thinking about the ethics of war: namely, Just War Theory.
I think the proper question with which to begin is the most basic one: namely, “Is the use of force ever justified?” According to the position I will term Absolute Pacifism, it is not. Absolute Pacifism holds that there is an absolute duty to refrain from using force in any context, whatsoever. I regard this position as a nonstarter: of course it is permissible, and sometimes obligatory, to resort to the use of force (e.g., when doing so is the only means by which it is possible to save an innocent life, including one’s own [provided that one is indeed innocent2]). I do not even regard Absolute Pacifism as a moral ideal - as a position that it is admirable, if not obligatory, to adopt - as some are disposed to do: it seems to me that there is nothing remotely noble or admirable in acquiescing to evil; in simply permitting the worst of humanity to inherit the earth.
There is a less extreme position that we might term Qualified Pacifism. On this position, it is specifically the use of force by the state which ought to be opposed. However, rather awkwardly for those who endorse this view, the very existence of a state is based upon its monopoly on the legal use of force: disobey a state in a sufficiently extreme and disruptive manner, and one of its agents will lead you into a cage at the point of gun. This is why some anarchists object to the very existence of states. But whatever its philosophical merits (and there are some), I consider anarchism to be straightforwardly untenable, as a practical matter: in order to secure peace and coordinate behavior effectively, any society consisting of more than a hundred or so human beings needs a state (or something more-or-less functionally equivalent). So, if Qualified Pacifism entails anarchism, that, by my lights, is sufficient reason to reject it. (By way of response, a Qualified Pacifist might insist that it is only waging war, specifically, that it is unacceptable for the state to do. However, if there is no in-principle reason in virtue of which states cannot use violence, or its threat, in order to protect citizens from one another, then surely there is no such reason in virtue of which they may never do the same in order to protect citizens from invaders.)
So, it seems to me that one must grant that, in principle, it could at times be permissible, and at times obligatory, for states to wage war. The major questions with which to concern ourselves in thinking about the ethics of war, therefore, are these: (1) what are the criteria which must be satisfied in order for a war to be just?, and (2) what are the constraints upon a state in conducting a war? For if one believes in objective morality at all, then one must grant that (a) war is justified only in a narrow range of cases and that (b) victory in war may not be sought by just any means whatsoever (despite the common growls about war being “hell”, no morally serious person could think that all of the rules of morality are simply suspended in the context of war).
Believing that morality is entirely about producing good consequences, consequentialists will hold that (i) wars should be fought when, and only when, this would lead to the best consequences and that (ii) they should be prosecuted by whatever means necessary to securing the best outcome. However, sophisticated consequentialists will generally think that, in practice, the state needs to be constrained by some principles - for it seems unlikely that things will generally go best if political and military leaders conceive of themselves as completely unconstrained by any rule apart from “produce the best consequences” (since that would, in effect, amount to giving them a blank check to do the best, by their lights - a particularly bad idea given all the cognitive biases to which we know all human beings are susceptible). There is a more general truth here, noted by Henry Sidgwick in The Methods of Ethics: namely, that the best consequences will most likely to be brought about by people who are principled rule-followers, rather than perpetual “utility calculators”.
Thus, consequentialists and non-consequentialists alike should hold that we need a framework for determining the conditions under which a war may be declared and the manner in which it may be prosecuted. The most influential framework of this sort in Western Philosophy has been Just War Theory, the basic idea of which can be traced back to Augustine of Hippo’s City of God but which was given its most influential articulation by Dominican friar Thomas Aquinas, in his Summa Theologica.
According to Just War Theory, six criteria must be satisfied in order for commencing a war to be just - the so-called jus ad bellum requirements. In order for a war to be just, it must, first, be waged in the pursuit of a just cause (classically, this cause will be essentially defensive in nature). Second, a just war must be waged by a legitimate authority (i.e., the entity declaring the way must have the authority to do so - as, for example, a tyrant or illegitimate regime3 could not). Third, the authority waging the war must do so for the right intention: namely, to achieve the just cause, rather than to (for example) merely use the just cause as camouflage in the pursuit of some other end (e.g., it would be unjust for a sovereign to wage war based on a just cause if the actual intention at work were to secure riches). Fourth, Just War Theory holds that there must be reasonable prospects of success in a war effort: that is, there needs to be a reasonable likelihood that a war will in fact achieve its aims (therefore, a war can, in principle, be unjust merely in virtue of being unwinnable by what would otherwise be the just side - for it would then be nothing more than the cause much pointless misery and death). Fifth, there is a proportionality requirement: the goods achieved by the war need to outweigh the evils that it will cause. And sixth, a just war is (by definition) undertaken as a last resort: there must no other, less awful, available means by which to achieve the just cause.
In the conduct of a just war, the jus in bello requirements apply. First, belligerents must practice discrimination between between military targets and civilians, and attack only the former intentionally (this allows for the possibility of causing civilian deaths as the foreseen, but unintended, consequence of some essential military objective achievable by no alternative means). Second, there is yet another proportionality requirement: foreseen but unintended harms must be proportionate to the military advantage achieved (so, for example, bombing a munitions factory located near a civilian neighborhood would be unjustifiable if this were not essential to advancing the war effort). And third, there is a necessity requirement: victory must be sought only be the least harmful means feasible (so, leveling a city in the pursuit of victory would be unjust unless victory were possible by no other means).
Each of the jus ad bellum and jus in bello requirements is in need of clarification and refinement, and there are extremely difficult questions with which any advocate of Just War Theory must wrestle. For example, with respect to the very first jus ad bellum requirement, we must ask what, precisely, constitutes a “just cause”. Can only defensive wars be just? It might seem so, initially; however, consider the now common judgment that the United States and other countries should have intervened militarily to prevent the 1994 Rwandan Genocide: such an intervention would not have been defensive, in the sense that the armed militias that perpetrated the genocide posed no imminent threat to the countries thought by many to have had a duty to intercede. And in the case of a defensive war: must those in the defensive state wait to be attacked before initiating a military offensive, or is preemptive military action permissible? If preemption is permissible, then how far in advance is too far - and how clear must be the intelligence on the basis of which such an act would take place?
Although Just War Theory raises at least as many questions as it settles, it nevertheless seems like the best starting point for thinking seriously about the ethics of war. For further investigation, a good place to begin is with the Stanford Encyclopedia of Philosophy’s article, “War”. Some influential works on Just War Theory in recent years include Michael Walzer’s Just and Unjust Wars: A Moral Argument with Historical Illustrations4 and Jeff McMahan’s Killing in War ;5 the former has been perhaps the most influential contemporary defense of traditional Just War Theory, whereas the latter aims to revise it (e.g., McMahan questions the traditional assumptions that (a) noncombatants on the unjust side of war are never liable to be killed and that (b) combatants on the unjust side have a right to kill in self-defense).
Arguably, given that humanity has yet to outgrow war, the fact that this ancient folly now threatens our long-term survival (in the age of nuclear weapons) means that careful thinkers ought to give far more thought to Just War Theory, as well as to the logic and the ethics of human violence and conflict more broadly.
I understand war as an armed conflict between states.
I take to be obvious that we can lose our right to self-defense if we acted sufficiently wrongly: a would-be murderer has no right to self-defense if his victim fights back.
Arguably, even a democratically-elected regime could be illegitimate, if sufficiently diabolical. Think of the Nazis, for example.
1997/2006, 4th edition, New York: Basic Books.
2009, Oxford: Oxford University Press.