The basic form of the larger question at hand is whether because one can effectively prevent or stop a sufficiently gross injustice assaulting some innocent person or persons within their proximity, such a person is therefore morally obligated to? My answer in a nutshell is: yes.

In fact, I’d assume this is a truism were it not that a good many people I (more or less) respect think otherwise. But, I figure we can get at the truth of it by way of an analogy. If I happened to be a very strong swimmer (it is my thought experiment, I can be what I like) and, while strolling alone along a deserted seashore, saw someone out in the relatively calm water in obvious distress and about to drown I take it to be self-evident that I ought to race into the water and save them. Several factors conspire to demand this. One, there is someone with a sufficiently grave need. Two, the need is morally licit. Three, I have the ability to meet that need. Four, there is no one else who can do so. five, if someone doesn’t meet the need, the person in peril will suffer a significant—and unjustified—harm. Six, my meeting this need will not unduly jeopardize other responsibilities I have. Seven, I have reasonable cause to believe I will be successful in meeting the need despite whatever obstacles stand in the way. Eight, all points taken together, I can expect more good than harm will come from my meeting the legitimate need.

The same question—and, I assert, the same answer—applies to a nation. Speaking from the US perspective, if one undeserving nation is under unjust assault by another nation, do we have an obligation to intervene and protect that nation? Once again, says I: Yes. Here, too, can implies ought.

I take my bearings from the casuistic moral framework of the Christian just war tradition. In the part of the tradition helping us determine when it is right to fight, we find the three criteria for assessing just cause: protecting the innocent, overturning an injustice, and punishing wrongdoing. Even in the presence of a just cause, the just war tradition recognizes that not just anyone can mobilize the nation to hostilities with another nation. Order is essential, therefore only a legitimate sovereign—the power or powers over whom there is no one greater charged with the care of the political community—can declare war. Moreover, even a sovereign who has determined there to be a just cause must seek to deploy force only with the goal of establishing peace. Peace, here, does not necessarily aim at the narrow ideal of establishing perfectly harmonious relations between formerly warring parties. Rather, the peace we have in view is more capacious. First, it might be merely an approximation of the ideal—at times it’s enough that no more bullets are flying. Secondly, the peace we are hoping to achieve is, in the first place, for the innocent people we are trying to rescue. While we ought to aim at peace—or some approximation of it—with our adversary, such an outcome is not only up to us. The enemy always has a vote.

These three requirements together—proper authority, just cause, proper intention—form what’s sometimes called the deontological criteria. This is to say, if these criteria are present, then addressing the just cause with the aim of remedying it is a moral duty—it is obligatory without regard of the consequences.

In addition to duty, there are sometimes special obligations that bind one nation to another. The US has defense pacts with more than 50 allies and partners. If our word is our bond, we are obligated—if to varying degrees—to respond to attacks against any one of them as if the attack were a “common danger” to both that nation and the US.

In addition to these formal obligations, there is probably also something to the old Pottery Barn rule that if you break it, you own it. While we need to be mindful not to fall into the trap of foolishly trying to justify sunk costs, the consequences of our shameful departure from Afghanistan ought to suffice in suggesting that there’s something to this rule that is salient.

There are limits to all this of course. One of those limits is baked into my framing of the question. I didn’t simply ask whether if there is a sufficiently gross injustice in the world ought the US to do something about it. I asked if the US can do something about that gross injustice, ought the US to do so.

This qualification, too, is grounded in just war morality. In addition to the obligating deontological criteria, there is a second set of criteria helping us to determine when it is right to fight. As already gestured to above, these include, first, assessing whether addressing the underlying just cause is likely to produce a greater amount of good than harm—and, conversely, whether not doing something about the just cause will result in more good than harm—second, evaluating whether we have any real prospect of actually redressing the existing wrongdoing, and, third, whether the use of force is the only likely means of doing so. Together, proportionality of ends, probability of success, and last resort form the prudential criteria. These are means of assessing the wisdom of doing one’s duty. In certain cases, the prudential criteria may overrule the deontological. Putting it in the most provocative way, there are times when doing what’s right is, well, the wrong thing to do.

Consider again our drowning man. If instead of relatively calm, as in the scenario described above, the water was tempest-tossed and the drowning victim was being dragged quickly out to sea, prudence might dictate that despite my being a strong swimmer it would be foolish to attempt the rescue. Of course, I might decide the extreme risk is worth taking. Precise—and swift—deliberation is essential, and I could only do as my conscious and judgment dictated. If we alter the scenario further and rather than being a strong swimmer it turns out that I’m a very weak one and happen to be in a leg cast then wisdom would resolutely militate against attempting rescue. With no practical chance of doing anything effective, I would not be risking my life but merely wasting it.

However, I want to be clear that I do not believe just because prudence overrules obligation that somehow the obligation ceases to be one. Not quite. I’m keen to make some space between my claims and what I take to be the basic Kantian premise that ought implies can. The opposite of my eponymous question, Kant’s phrasing insists that if a particular action is impossible for an agent to perform then the agent is under no obligation to perform it. Against this, I want to suggest that the obligation still remains; it’s just that it cannot be met. In some cases, there may be no moral culpability attendant in my not being able to carry out the obligation. In other cases, there might well be. If the reason I could not perform the rescue is only because I was too blindly drunk to do so, I may be deemed morally blameworthy indeed.

The other argument against the proposition that can implies ought is that of personal—or national—interest. Again, the beach: I may be a great swimmer but if I’m alone with my young child on the otherwise deserted beach and the conditions are such that attempting rescue is mortally perilous to me, then not just prudence but parental responsibility might dictate I refuse to try. In this scenario, it should become clearer that it need not be a question of whether I have a duty to attempt the rescue or not. The duty to rescue the drowning man is now conflicting directly with my duty to not put my child at undue risk. I am not shirking responsibility, I am weighing one set of responsibilities against another set and, finding that it is impossible to meet both, I determine that I have grave reasons to give deference to the one set over the other. The accompanying sentiment here should be one of tragedy.

What I am trying to champion here is a modification of the so-called Spiderman ethic: with great power comes great responsibility. My thesis is that there is always a strong presumption that if there is someone in danger then it is obligatory that I do something about it, conditioned only on whether I have the capacity to. If I do not have the capacity, it does not mean I am simply off the hook. It means that in this regard I am a failure. This carries an implication: to the degree that we are reasonably able, we ought to increase our capacities. Of course, sobriety is called for. At a personal level, there are many ways to help those in need. But not everybody can be expected to cultivate all the financial, intellectual, physical, medical, martial, and other capabilities required to help our neighbors in any crisis they face. Obviously, too, our obligations are primarily to those special obligations unique to who we are: they radiate outward from our immediate family to our extended family, our friends, our neighbors, those to whom we have made promises, those encompassed in our sworn oaths, our countrymen, etc. In some situations our greatest duty might well be owed simply to the person immediately in front of us. But to the degree that we are able, within reason, to cultivate the capabilities of meeting possible obligations without compromising existing obligations we ought to.

Of course, it’s more complicated than even this. Surely there are occasions where I risk a great deal of harm to those I have special obligations in order to help others in great need. To begin with, for instance, while it is my fatherly duty to make sure my children have enough to eat, that duty does not extend to making sure they have everything to eat that they might like. If my neighbor is suffering a deficit of food, I certainly ought not to give my children luxury items instead of helping my neighbor have basic sustenance. If the situation is such that my neighbor is starving and food is in scare supply, then it is right that my children my tighten their belts—and that I tighten my own more tightly still than theirs—if that is the only means to helping our neighbor survive.

If true of individuals, then it is true, too, for nations. While it is also true that the chief moral obligation of any particular sovereign is to his or her own people, this obligation is not absolute. A nation should cultivate those capacities that they are able to cultivate in order to be of use to other nations in need.

Speaking of the United States, providence and ambition have allowed the US to gather to itself vast stores of power and security. This is not simply the result of having friendly neighbors above and below and two vast oceans to either side. It has been a choice. And it is a choice, too, that we have not simply horded this power to our own good. America, for all her ills, has been a force for good in the world. This has not merely been altruism at the expense of national interest. Doing good in the world, for the world, rebounds to our own good. Besides much else, an ordered community of nations aligned to a common good forms the outer perimeter of our own security. But spending our power on the welfare of other nations also makes the power we have sufferable to those beneath it.

The US, like any nation, has as its first obligation its own citizens. But there have been times—and there will be times again—when we have helped other nations at great peril to our own. This is as it should be. This does not mean that we do not encourage other nations and other regions to take the lead on addressing their own and regional matters. We should, and we should help them do so. Nor does it mean, to riff on the Bard, that just because we have a giant’s strength that we use it like a giant—throwing our weight around just because we can and unduly interfering in others affairs. As I recently heard from someplace: just war’s just cause doesn’t mean we can be belligerent just ‘cause we can. Or something like that.

There’s much more to be said on all this. I have tried only to sketch out some initial thoughts. But, the web-slinging moral code aside, the just war moral framework, and our greater Greco-Roman and Hebraic inheritance in which it is grounded, have rightly shaped our character–individually and as a nation–so that we have been the kind of people who run the kind of nation that is committed to helping where we can.

And where we can, we ought.