Over the last few years there has been a sharp change in the rhetoric of the Catholic hierarchy on the issue of nuclear weapons. During the Cold War, even as Church leaders warned of the terrible destructive power of nuclear weapons and their profound moral problems, for the most part Catholic leaders accepted”or at least tolerated”the need for such weapons. Not so today. In recent years, members of the hierarchy have issued blunt statements insisting on the imperative of near-term nuclear disarmament. These statements have revealed a disturbing inattention to important aspects of how nuclear weapons would be used and, more broadly, to the profound and beneficial implications of nuclear weapons for international stability. Given the Church’s obligation to moral seriousness and the gravity of the issue, this matter deserves more care and reflection than these members of the hierarchy have given it.

Church leaders have been very active recently in insisting on the moral obligation to meaningfully pursue nuclear abolition. At a deterrence conference sponsored by the United States Strategic Command in July 2009, Archbishop Edwin O’Brien called the Catholic task “not to make the world safer through the threat of nuclear weapons, but rather to make the world safer from nuclear weapons through mutual and verifiable nuclear disarmament.” Writing in support of the new Strategic Arms Reduction Treaty signed by the United States and Russia in April 2010, Francis Cardinal George described the pursuit of ridding the world of nuclear weapons as “a moral imperative.” Archbishop Celestino Migliore, until recently the Holy See’s representative at the United Nations, has been especially insistent on the need for nuclear disarmament. Even Pope Benedict XVI, in his 2006 World Day of Peace message (and again in his 2010 message), dismissed those who count on nuclear deterrence for their security as holding “a point of view [that] is not only baneful but also completely fallacious . . . . The truth of peace requires that all . . . agree to change their course by clear and firm decisions and strive for a progressive and concerted nuclear disarmament.”

Why the change from a guarded acceptance of nuclear deterrence to clarion calls for disarmament? The primary reason given is that the conditions that compelled the Church in the 1980s to give limited toleration to some forms of nuclear deterrence no longer exist. Clearly this assessment has been spurred on and strengthened by the high-profile campaigns for nuclear abolition of the last few years. Yet, especially when compared to the sober caution of leading abolition advocates such as George Shultz, William Perry, Sam Nunn, and Henry Kissinger, the much more radical position of the churchmen must be drawn from a more fundamental analysis than a mere change of political conditions. Indeed, the argument from church leaders for prompt nuclear abolition appears to derive quite directly from an analysis based on classical just war theory. As Cardinal George has written, the use of nuclear weapons “as a weapon of war is rejected in Church teaching based on just war norms.”

This is a bold claim”and one with substantial merit”but is it so completely true that it would logically require the complete abolition of nuclear weapons?

The argument proffered by the churchmen is as follows. For the use of force to be morally tolerable it must be discriminate”civilians may not be the object of direct, deliberate attack”and it must be proportionate to the evil confronted and the good achieved. In light of these premises, an empirical claim is made: that nuclear weapons, by their very nature, cannot be used in a discriminate and proportionate fashion and thus are illegitimate. As Archbishop O’Brien has argued, nuclear weapons “cannot ensure noncombatant immunity and the likely destruction and lingering radiation would violate the principle of proportionality.”

This judgment is grounded in an empirical assessment that escalation is highly probable in a nuclear exchange and therefore that the demands of proportionality cannot be satisfied. As Archbishop O’Brien puts it, “Even the limited use of so-called ‘mini-nukes’ would likely lower the barrier to future uses and could lead to indiscriminate and disproportionate harm. And there is the danger of escalation to nuclear exchanges of cataclysmic proportions.” Nuclear weapons, in short, cannot be used discriminately and proportionately, both because of their inherent destructiveness and because their use is so likely to incur further, catastrophic damage. Therefore, because nuclear weapons cannot be used morally in warfare, they have no justifiable use and warrant elimination.

This argument has natural force. Nuclear weapons are immensely destructive, and their use carries grave risks of further escalation. Yet the analysis that Archbishop O’Brien and other churchmen provide is highly problematic. The most glaring flaw is the intermixture of firmly grounded elements of Catholic moral teaching with highly disputed”and, in some cases, erroneous”analyses of military conflict, national decision making, and the legitimate uses of force. A deeper problem is that the churchmen’s analysis disregards the profoundly serious dilemma of how best to preserve peace”a dilemma that has been with the Church at least since Ambrose and Theodosius sparred over resistance to the barbarian invasions. This dilemma between what safety and stability require on the one hand and what Christian love demands on the other deserves a more sober and respectful treatment.

Archbishop O’Brien, whose speech at the Deterrence Conference in 2009 represents perhaps the fullest exposition of the logic of this point of view, begins his argument for the inherent immorality of nuclear arms by stating that nuclear weapons “cannot ensure noncombatant immunity” and so are intrinsically illegitimate weapons. But this is an unreasonable standard even under just war theory, which requires only that violence not be deliberately directed at noncombatants. Indeed, no weapon can “ensure noncombatant immunity.” Artillery can be turned against enemy positions or a crowded neighborhood, submarines against warships or hospital ships, rifles against enemy soldiers or captured civilians. Moreover, systems fail. Even today’s precision-guided munitions go awry because of technical error or are targeted based on inaccurate intelligence.

Nor is the ability to ensure noncombatant immunity merely a problem of intent or better systems. Because conflict is competitive and adaptive, adversaries cannot always afford to dedicate sufficient focus to avoiding noncombatant injury without sacrificing their legitimate objectives. In the Second World War the Allies felt compelled to conduct saturation attacks and night bombings on German cities because of the formidable German defenses. (And this leaves aside the deliberate general bombings of Japanese cities to suppress industry and break Japan’s national will.) Similarly, the United States pursued unrestricted submarine warfare against Japan in part because it could not safely or reliably distinguish innocent from war-supporting supply ships. Further, adaptive adversaries often will deliberately intermingle civilian and military targets to complicate attacks by an opponent attempting to abide by the principles of just war. One can see this clearly in the use, in Iraq, of mosques as defensive positions. For these reasons a fairer standard for judging the legitimacy of weaponry would be that the use of any weapon must be proportionally correlated to a just goal.

But Archbishop O’Brien argues that nuclear arms are distinct among weaponry because of their “likely destruction and lingering radiation” and because even smaller-scale nuclear weapons “would likely lower the barrier to future uses and could lead to indiscriminate and disproportionate harm.” Cardinal George contends that “the horribly destructive capacity of nuclear arms makes them disproportionate and indiscriminate weapons that endanger human life and dignity like no other armaments.” In other words, nuclear weapons are “likely” to be so destructive that their use cannot be reconciled with just war principles; and the use of nuclear weapons, however small and restricted, involves inherent escalatory pressures that would raise the probability of further employment and catastrophic destruction. While both arguments have considerable elements of truth, they are too incomplete”and thus far too misleading”to serve as bases for the firm moral judgments drawn.

For it is simply not true that nuclear weapons are inherently incompatible with just war principles. Very highly destructive weapons, including nuclear weapons, can be targeted discriminately, provided the target is militarily significant and sufficiently separated from innocent parties. Under these traditional law-of-war guidelines, permissible targets might include missile silos, air bases, submarine ports, ground forces and their installations, leadership redoubts, and other militarily significant objects and facilities large or isolated enough to justify attack with highly destructive weaponry. Indeed, because of advances in the accuracy and reliability of systems, such targets can be attacked today with nuclear warheads that produce a lower yield and cause less destruction than those mounted on the highly inaccurate bombs and missiles of the early Cold War, thereby lessening the direct secondary effects of a strike. Yet even higher-yield nuclear weapons can be directed at isolated targets far from population centers. For instance, the American early-warning radar located far from any significant populace in northern Greenland near Thule surely would have been a legitimate military target for the Soviet Union. Other factors such as the time of the strike”and whether the weapon is detonated in an air or ground burst”also can minimize the secondary consequences. This is not to minimize the horrendous destructiveness of nuclear weapons but to emphasize that even extremely destructive weapons can be used to strike militarily significant targets while minimizing civilian casualties”in other words, discriminately.

With respect to the criterion of proportionality, we must also consider the role of necessity in a just cause. If the destruction of a target is critically important, it may be permitted under classical law-of-war doctrine if the ancillary damage is not intended and its costs do not outweigh the legitimate object achieved. This is known as the principle of double effect, to which the churchmen do not appear to give adequate weight. This rule states that actions causing serious damage may be permissible if they are a secondary effect of actions taken for a justified end. The rule distinguishes legitimate actions directed toward morally licit goals that incidentally cause serious harm from illegitimate actions that instrumentally cause harm to achieve a good end. The rule also emphasizes the principle that such damage inflicted must be proportional to the evil threatened and the good achieved. The Second Vatican Council, in Gaudium et Spes , gave self-defense as the archetypal valid reason for exercising this moral right.

Logically, therefore, weapons of great destructiveness could be used”including, potentially, against highly important targets not isolated from noncombatant populations”in the cause of defending against grave evils. During the Second World War the Allies frequently attacked Axis military and war-supporting facilities in highly populated areas (including in occupied countries such as France and China) because that was the only plausible way to achieve their legitimate objectives. Earlier, it was an accepted practice that a city resisting a siege would endure sack and pillage in the wake of its conquest. If such a city were allowed clemency after resistance, it was agreed, military operations, including legitimate ones, would be impractical because a fortified city could hold out and frustrate an army’s advance without consequence. More recently, the United States has stated consistently that it would not target adversary populations per se with its nuclear forces, although, in fairness, this would be of vanishingly modest comfort to those anywhere near legitimate targets broadly defined. This is not to minimize either the moral complexities associated with this rule or the dangers of nuclear use but to point to examples in which highly destructive threats and practices have been seen as justified because they were seen as necessary for the pursuit of just ends.

Archbishop O’Brien’s rejoinder to these arguments is that any nuclear employment would carry too great a risk of further use. This is a decidedly prudential judgment and, in key respects, dubious. It is highly disputable that any use of a nuclear weapon, divorced from any other considerations, is the primary determinant of whether a nuclear or military exchange will result. It is not primarily the destructiveness or physical nature of a weapon that determines the risk of escalation but rather other factors such as the danger posed to the core capabilities and interests of an adversary. And so, while nuclear (as well as nonnuclear) strikes to suppress the nuclear capabilities of an adversary would intensify pressures to “use or lose” these forces, many types of nuclear strikes, particularly those more defensive or signaling in nature (and thus more justifiable), would be considerably less likely to do so. Conversely, weapons with significant utility in disabling an opponent’s war-fighting capabilities are more likely to cause escalation than those designed solely to inflict damage. (Indeed, it is interesting to note the tension between traditional just war theory, which sought to channel violence toward military targets and thereby limit the scope of conflict, and the world of nuclear deterrence, which is heavily influenced by fears that such a focus may actually increase the likelihood of broader nuclear war.) A classic example is the escalation of competitive mobilizations at the outset of the First World War. More recently, the forward-leaning and primarily conventional “maritime strategy” of the U.S. Navy in the 1980s may have been more likely to prompt the Soviets to escalate to nuclear use than was the 1970s U.S. strategy to conduct limited nuclear strikes against isolated and relatively unimportant Soviet targets to terminate a large-scale war.

For these reasons, conventional forces, especially those of the United States, may be more likely to raise the chances of escalation because the United States and its allies operate with relative impunity. Indeed, this near-complete discretion is a major reason countries such as Iran and North Korea are attracted to nuclear weapons: Such weapons could deter the United States from exercising its conventional capabilities.

Fundamentally, the dangers of escalation stem more from strategic considerations of threats to leadership control, military forces, and the survival of the nation and less from the particular characteristics of the weapons used. This is not to understate the dangers of escalation that nuclear use would entail but rather to point out that weaponry is only one factor in such considerations, and likely not the most important.

This discussion only scratches the surface of Archbishop O’Brien’s analysis. The key point is that the claim that nuclear weapons can never be used in a morally justifiable fashion does not stand up to scrutiny. Nuclear weapons can be used in ways that, while possibly inadvisable for other reasons, comport with classical just war principles.

But there is a very real tension between what nuclear weapons do and the obligations of Christian morality”a tension that should cause unease not only among moral strategists but also among strategic-minded moralists. This tension stems not primarily from the particular physical characteristics of nuclear weapons or their unique destructiveness but from their role as the ultimate keepers of the peace”a peace that Christians should prize and encourage, but one that also has its roots in, to put it bluntly, terror.

What is this tension? Human beings have always battled each other. Recent research suggests that a substantial fraction, perhaps even as high as a half, of prehistoric deaths were caused by violence. While better, civilized man has remained enormously destructive. The Thirty Years’ War is supposed to have killed a third of the population of the Holy Roman Empire, while the two great wars of the first half of the twentieth century killed nearly 100 million people. And yet, abruptly, after 1945 wars between advanced nations have essentially stopped, and those that have taken place have been very limited. Why?

No doubt economic development and the spread of liberal civilization have played a role, as has the exhaustion that followed the great wars of 1914 and 1939. But these forces are ill-placed to explain such a broad and consistent trend, if for no other reason than that people have many times before been rich, civilized, and exhausted. Moreover, since it requires only one party to cause a major war, it seems implausible that all people are now so satisfied and upright that they are willing to forswear the use of force to gain their ends. The more plausible explanation for the trend is that the introduction of nuclear weapons has made the prospect of war so terrifying, and its consequences so manifestly incommensurate with any plausible gains, that such weaponry has deterred even the aggressive and the rapacious from starting a war. The result has been a long peace.

For the Christian, and for all people of good will, the result is cause for rejoicing. The absence of war is surely a good even if it is not grounded in the truest peace, that of love. Nor are the benefits confined merely to the absence of conflict. Because of the greatly reduced likelihood of war, countries can dedicate far more substantial resources to social needs and development”a good the pope explicitly noted as an important reason for disarmament in his 2006 World Day of Peace message. Moreover, the danger of militarism is lessened, and liberal democratic systems, traditionally vulnerable to the criticism that they are ill suited to war, are more resilient.

Yet Christians must be uncomfortably aware that this peace is, after all, the “sturdy child of terror,” as Churchill put it. Indeed, the more credible the nuclear threat and the more devastating its consequences, the more secure this peace. At root, the effectiveness of nuclear deterrence rests on making a prospective attacker fear the most baleful and awful consequences, while the moral direction of Christianity is a progressive invocation to love and sacrifice. It seems doubtful that a stability grounded in terror can be fully reconciled with the law of love, at least with finality.

But while nuclear deterrence can hardly be expected to satisfy counsels of perfection, Christian morality is not confined to the aspiration for perfection. Christians are required to avoid evil and do good, as understood by the law of reason and in recognition of the reality of sin. By this more worldly standard there is reason to think that, even if it cannot be perfectly reconciled with Christian moral demands, certain kinds and postures of nuclear deterrence can be made tolerable or even acceptable under just war theory.

For instance, while much discussion of the morality of nuclear weapons focuses on the problems posed by their use, less has gone toward the other pole of just war theory” ius ad bellum . Ultimately, judgments as to the legitimacy of actions taken in war cannot be completely segregated from the rectitude of the cause for which violence is undertaken. Surely the use of weapons of massive destructiveness for aggressive or discretionary purposes can hardly be defended, but their use in certain manners for the defense of legitimate national autonomy against an aggressor, in the most extreme circumstances, seems more readily justifiable. The latitude granted to the weakened and supine West against Stalin, or to Britain in 1940, or even as far back as to the European powers against the Turks, Vikings, and Arabs seems legitimately greater than that available to those conducting wars of lesser necessity.

Perhaps, then, limiting the purposes for and conditions under which nuclear weapons may be used, such as in “extreme circumstances,” as the 2010 U.S. Nuclear Posture Review suggests, could contribute to a morally tolerable form of nuclear deterrence. In terms of ius in bello , certain constraints on the use of nuclear weapons might also be imposed. Warnings, for instance, could be strongly encouraged to enable the civil population to avoid harm. Tolerance might be given in extreme circumstances to limited, essentially demonstrative, employment of nuclear weapons against targets isolated from substantial noncombatant populations. If such efforts are unavailing, targeting that focuses on those in power (and so responsible for the extreme measures being taken) and what they value, or on essential military facilities, as opposed to the general population, might also be tolerable in some particularly grave situations. In all cases the purpose of the strikes would be to prevent some grave evil, to deter further aggression or escalation, and to bring the war to a tolerable conclusion as rapidly as possible.

It must be admitted, however, that even if such restraints were imposed, nuclear deterrence would, in all likelihood, still rely on the threat of cataclysmic destruction. Indeed, in all honesty, the possibility that conflict might escalate to such a level lies near the root of the effectiveness of nuclear deterrence. It is precisely the prospect of such general destruction that so clearly makes any aggression not worthwhile. Thus, for instance, it was the vision of a general exchange between the United States and the Soviet Union that so terrified General Secretary Leonid Brezhnev that, visibly shaking, he resisted pushing the simulated release button during a military exercise in the early 1970s.

While we can take steps to minimize the tension, the fact is that we live with a paradox. The stability and peace we have enjoyed for sixty-five years, even in the face of a great and hostile Soviet Union, rests on the profoundly troubling threat to wreak catastrophic violence. It would be easy to say that those dark days of the Cold War are over and so we can, on strategic grounds, abandon nuclear deterrence. But this would be the height of imprudence. The history of world politics, at least, is not over, and the era of untrammeled U.S. military superiority is fading. Even thoughtful advocates of a world without nuclear weapons admit that the conditions necessary to allow abolition do not currently exist and would require fundamental transformations in the world order. In the meantime, nuclear deterrence continues not only to deter aggression but also to remind all that investments in military power are of decidedly limited value”an effect that has had and continues to have tremendous ramifications for interstate relations, the allocation of resources, and social and political life throughout the world.

This is not to luxuriate in this paradox so central to the modern world but only to give grounds for asking that church officials deal with the matter with more care and caution than they have in some cases. For instance, Pope Benedict, whose writings and speeches have captured with unique sobriety and wisdom the nature of life in the modern world and the solution that Christianity gives to our mortal condition, has said: “What can be said, too, about the governments which count on nuclear arms as a means of ensuring the security of their countries? Along with countless persons of good will, one can state that this point of view is not only baneful but also completely fallacious.” What can be said to such a dismissive statement, which questions even the good will of those who value the benefits of nuclear deterrence? Perhaps one can ask that the pope and other churchmen consider that those who defend nuclear deterrence do so not from evil intent or in an unreflective way but because they value peace and stability and because they fear a world in which violence can again be a more attractive tool of statecraft.

The Church should never, for any reason, quiet its call to sanctity, least of all for reasons of state. But for the Church to make a focused, concrete call for a specific goal such as nuclear disarmament is to go beyond that call; it is to make a concrete judgment about worldly affairs that presumably takes into account practical and prudential factors along with moral ones. In such an instance, the validity of the Church’s analysis of these worldly factors directly determines the validity of the overarching judgment. Given the significant weaknesses in the churchmen’s analysis of the nature of nuclear weapons and the characteristics of their possible use, so must the concrete call for expeditiously abolishing nuclear weapons be correlatively weakened.

Without question, Christians must strive for peace and encourage the development of a society built on love and charity rather than on fear and self-interest. But precisely how to reach such a goal in a fallen world is a matter that, especially when considerations of war and death are involved, must be addressed not only with fervor and dedication but also with sobriety and prudence. In addressing matters of such consequence and difficulty as the role of nuclear weapons in preserving and restoring peace, no less can be expected from those who serve as the moral shepherds for those journeying in this fallen world.

Elbridge A. Colby has served in several national security positions with the U.S. Government, most recently with the Department of Defense and the Congressional Strategic Posture Commission. The views expressed herein are his own and do not necessarily represent the views of any institution with which he is affiliated.