In Episode IV I provided an overview of Just War’s jab and jib frameworks. I described the moral guidance of just war as both a moral spur and moral restraint. Regarding the jab—which determines when it is right to fight—the spur emerges from what can be called the deontological criteria. As we’ve seen, these include proper authority; just cause—protecting the innocent, taking back what’s been wrongly taken, and punishing evil; and right intent. I wrote that when a proper authority, or sovereign—defined as the person or body over whom there is no one greater charged with the care of the political community—determines that the innocent are sufficiently threatened, a significant-enough injustice has occurred, or a sufficiently grave evil needs to be punished then they are morally spurred to do something to rectify the situation, possibly including the deployment of military force. In most cases this is something more than permission, it is a obligation. The restraint, however, as I pointed out, comes with the just war assertion—as a product of a Christian realism—that the question of whether to embark upon a justified war is not, in the final sense, merely a moral question. The just war moral framework has, built right into it, the understanding that moral judgements cannot, they must not—that’s to say ought not—be made in abstraction, deracinated from certain cold, unrelenting, and frustratingly immovable facts. There has to be a place for prudence. Wisdom matters.

Recognizing this, I stressed, is essential. The just war moral framework demands that principles and facts be mutually interdependent. Each must influence and inform the other. Christian norms will demand that in light of the fact that our neighbor is being assaulted we have a duty to come to his rescue. But facts, themselves, will help determine how principles are pursued, even to the point of overruling duty. This is to accept that the just war framework is not a simple checklist by which one can simply determine, if certain requirements are ticked off a list, that war will be. Rather, the just war is a tool to promote casuistic—case driven—moral reasoning. Different cases, grounded in diverse contexts, might require different kinds of moral action.

Here we come to the second set of requirements: the prudential criteria. Tracing their historical pedigree isn’t straightforward and it’s unclear when the prudential criteria entered, in any kind of explicit way, the just war frame. James Turner Johnson, the preeminent historian of the just war tradition, doubts, contrary to some, that they reach back as far as the Neoscholastics. He suggests instead that they emerged quite a bit later, springing from the same uneasiness with modern war that spawned so-called modern-war pacifism. Nevertheless, whatever their provenance, the Christian realist needn’t have a principled objection to their inclusion in just war thinking. They play an important, if secondary, supportive role to the primary deontological criteria. It is right that a political sovereign, having already determined in a particular situation that the use of force is justified, must now determine whether force is in fact wise to undertake.

While the tabulation varies, I count three primary prudential requirements: last resort, proportionality of ends, and probability of success. In the first place, last resort is perhaps best introduced by briefly stating what it’s not. Last resort doesn’t mean that every single option short of force must be actually tried, tested, and evaluated. It does mean that every reasonable alternative has been given due consideration. This needn’t be overly belabored. Just as it sometimes immediately obvious that nothing short of lethal force is likely to prevent the homicidal escaped convict who has just kicked in your door with a machete in hand from harming you, so too can immediate circumstances sometimes make plain that nothing short of a resort to war will stop an adversary who has already cast his vote for war. In such cases, it’s not that other options are simply ignored, but that a kind of “instant on-the-spot judgment” has already been made.

Understood in the right sense, last resort can be seen as something more than merely a matter of prudence. It should be self-evident, even in the face of justified causes, that if any option short of war can be reasonably expected to sufficiently protect the innocent, requite an injustice, or punish evil then that option should be pursued instead of war. This isn’t merely wise, it’s morally required. But this assertion plays out in another, more kinetic, way as well. It may be that a more limited deployment of force can prevent the escalation of force to a full-blown war. As Dan Strand, now a professor of ethics at the US Air War College, cautioned sometime back: “If we look at…recent humanitarian catastrophes—Syria, Darfur, Rwanda, Bosnia—earlier intervention in a limited but effective way could have headed off or greatly mitigated those tragedies.” Red lines could have been enforced with limited airstrikes, limited—and speedy—insertion of small forces could have prevented genocide, and the like. When equally effective in all the important ways, a little fight is always preferable to a big fight.

Indeed, last resort ought even to inspire particular kinds of behaviors that help avoid the necessity of even small-scale fights. For instance, one way to avoid a fight is to effectively deter it. By cultivating formidable degrees of military power, martial prowess, and the believable willingness to deploy it in support of particular interests and values, a nation might deter an adversary’s aggression or even compel their cooperation. Of course, hard power is not the only resource. Last resort ought also to prompt a nation to establish the capacity for deploying effective soft-power assets. A powerful nation whose foreign policy treats other nation’s generously, that gives them their due, and that doesn’t treat every act of international exchange as a zero-sum game will go a long way in making their power sufferable to those beneath it. The effective deployment of such hard and soft power resources benefits greatly when a nation has done its homework. Deterrence, coercion, and persuasion are only effective if we know how a particular adversary can actually be deterred, coerced, or persuaded. Cultural literacy is a must. We ignore the particularities of nations, their leaders, and their people at our peril. It  In a phrase, then, a nation that takes the wisdom of last resort seriously ought to have a reputation that can convincingly described by the old adage: no better friend and no worse enemy.

The next two prudential criteria link directly to the deontological criterion of “right intent.” As we’ve seen, in the larger sense the intent behind a justified use of force is peace. In the first degree, this peace is for the victims that need rescue—which occurs when their physical welfare and other components of their ability to flourish have been secured, when injustices have been requited, and when the guilty have been properly punished. In the second sense, this peace is aimed at establishing the conditions necessary to reconcile with the enemy. Both kinds of peace are most often best guaranteed through a decisive victory. An enemy who knows they have been licked is typically more amenable to changing their ways than one who does not. This is the ideal, and not every war aim is necessarily so ambitious. “Victory” may be defined merely as getting a given regime to stop barrel bombing their own people.

The criterion of proportionality is found in both the jab and the jib. Here in the jab, proportionality is focused on the ends determined by the intention of achieving peace through a decisive victory. The question being asked is whether the goods that  will come from pursuing this end are likely to outweigh the harms that will come. Similarly, it also has to be asked whether the goods of not pursuing peace through a decisive victory—that’s to say, the goods of not fighting—will outweigh the harms of not fighting. Goods and harms are sometimes very difficult things to weigh.

Like proportionality, “probability of success” also links to right intent. Here, whatever the war aim—however ambitious or limited—prudence dictates that you ought to have some likelihood of being able to achieve it. This is because, to say the obvious, even a limited use of force is destructive. The expenditure of national treasure—weighed both in resources and in blood—ought always to be a morally legitimate expense. A sovereign might spend the lives of their people, but they must never waste them. This isn’t to say that one must always only fight fights that they know they will win. The 300 who stood at Thermopylae prove the legitimacy of delaying actions and of inspiring others to rally to the fight. Existential threats, even when the hope of victory seems remote, can also be legitimate.

This is a rough overview of the prudential criteria as I understand them. It is important to emphasize again how they are to be used. As touched on above, following Jim Johnson, the prudential criteria ought to be understood as being in support of the primary deontological requirements. As Johnson argues, “this understanding retains the fundamental logic and the priority o the classic just war criteria while providing a structured role for the prudential exercise of statecraft.” It preserves the presumption against injustice I’ve argued for earlier.

Against this proper use, the prudential criteria can instead be commandeered to displace the deontological requirements. By elevating last resort, proportionality, and reasonable hope of success to main theme status within the just war frame, this scheme can downplay the duty promoted by the deontological criteria—rescue of the innocent, the overturning of injustice, and the punishing of evil—and instead privilege the avoidance of war except for extreme cases. Perhaps the main tactic for doing so is the magnification of the evils to be expected from a resort to force to such a level that, practically speaking, it can never appear sufficiently wise to sanction that resort to force. In this way, the prudential criteria is made to collude with a presumption against war, transmogrifying the just war tradition into a patsy for functional pacifism.

Pushing against this misuse of the tradition isn’t to say that wisdom ought never to overrule duty. The use of force, even justified force, may sometimes be unwise to undertake. Not everything that is morally permitted—or even obligatory—is prudent to do. But this is not the same thing as saying that the force that turns out to be imprudent to use is therefore also unjust.

Indeed, it is likely just the opposite. There are times when we may determine that is it profoundly unwise to fight a fight that ought to be fought. But—as the just war tradition is at pains to instruct us—because a fight ought only to be fought when the innocent are threatened, when an injustice has occurred, or when evil needs to be punished, the motivation for such fights is justice. Therefore, to not fight the fight that ought to be fought is to allow an injustice to continue—and it is to allow the innocent to continue to suffer it. It may be a fact that it is plain to see that no effort to save our assailed neighbor has any chance of being successful, but, rather, is likely to escalate the horrors, exacerbate injustices, and lead to the harm of an unbearable number of other innocents. In light of such facts, it may be that we stand down. It may be, in the way of this broken world, that this is the right thing to do. But standing down in this situation—because we have not been able to fulfill our duty to our neighbor—can only be understood as a tragedy.

Prudence sometimes commands restraint. Wisdom might reveal that we have a duty to stand down from doing our duty. Reality–and the demand that facts make on our moral action–sometimes bites. The crush is palpable. Tragically, realism and moral realism sometimes join in a similar orbit. How this can be is a matter for another time. In the meanwhile, God help us.