Traditionally, moral theologians have argued that to use military force justly, one must have a just cause; the use of force must be the last resort; success must be probable; the means must be proportionate; and the military action must be by a legitimate authority.
As the Obama administration prepares to respond to the use of chemical weapons in Syria, what are the ethicists saying about the morality of military intervention? In this article, I will examine their views about whether intervention in Syria fits the criteria of a just war. Links are provided to the more complete thoughts of each expert.
No moralist supports the actions of the regime of Bashar Assad or the use of chemical weapons, and no one is an enthusiastic supporter of the rebels. Under these circumstances, is there a moral case for intervention?
Although he acknowledges that nerve gas is a terrible weapon, Stanely Hauerwas of Duke Divinity School argues  that there is no moral justification for intervention: "Syria isn't attacking the United States." Self-defense would be the only justification for the use of force.
But most other moralists recognize a responsibility to protect innocent people, and they support their argument by pointing to the United Nations' doctrine of the Responsibility to Protect (R2P) , adopted in 2005. This would include thinkers like Matthew Shadle  of Loras College, William Galston  of the Brookings Institution, Drew Christiansen  of Boston College, Rabbi Michael Broyde  of Emory University, Kevin Ahern  of Manhattan College, Tobias Winright  of St. Louis University, and Maryann Cusimano Love  of The Catholic University of America.
While President Barack Obama drew a red line at the use of chemical weapons, Christiansen and Andrew Bacevich of Boston University do not see  any intrinsic difference between killing innocent people with chemical weapons and killing innocent people with conventional weapons. If chemical weapons are repeatedly used, Christiansen said he sees a reason for intervention. But their single use "doesn't weigh up compared to those who should have been protected and haven't been, and those who still need protection."
But even those who believe in the responsibility to protect innocents say more is required if the just war criteria are to be met.
"From a just war perspective," Winright writes, "I do not see how military intervention is morally justified if we take into consideration -- as we must -- other criteria, besides only just cause, of the just war tradition." Most agree with him.
Under the just war theory, war is the last resort after diplomatic and other means have failed. Many moralists do not believe all other options have been exhausted in Syria. "What is needed is a concerted and sustained effort to aid Syria's civilian population," Christiansen writes.
He has specific suggestions: "First, efforts should be undertaken to negotiate access for the International Committee of the Red Cross and other humanitarian organizations to population in need. Secondly, charges against the Assad regime should be brought in the International Criminal Court and other available venues to insure justice for its victims -- at least in the long run. Thirdly, serious attempts should be made to train and arm trusted secular and moderate religious elements in the resistance to Assad."
Others say diplomatic means have not been exhausted. Ahern quotes Hans Blix, the former chief U.N. arms inspector for Iraq from 2000 to 2003, who "strongly urges more diplomatic actions through what he sees as the only legitimate global authority," the United Nations.
Shadle also believes a "negotiated settlement with U.N. backing is currently the more just course of action, and only then might a coordinated international intervention to force the major Syrian groups to comply be justified."
Ahern agrees: "We must work with all parties involved to try to come to a creative diplomatic solution. We must examine our broader policies and the role played by our allies in the region in this conflict. It's been done before and can be done again."
On the other hand, Galston believes "prospects for diplomatic progress appear slim, and the Syrian government's recent use of poison gas against a rebel stronghold probably derailed diplomacy indefinitely." He is pessimistic about a peaceful resolution: "So it's reasonable to conclude that if we do nothing, nothing will change, and the slaughter of civilians will continue indefinitely."
Possibility of success? Proportionality?
Moralists are comfortable articulating theory, but they are hesitant to predict the results of a military action. Yet that is necessary if one is to estimate probability of success or whether the harm will be proportionate to the good accomplished. These "are the hardest Just War criteria to meet in the Syrian case," writes CUA's Love. She cites the concerns of Ambassador Ryan Crocker, whose diplomatic posts include Afghanistan, Iraq, Pakistan and Syria, as well as Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, that any military intervention may fail.
Broyde believes "options that bring peace and protect the innocent are to be favored when reasonable people think that they are likely to work in fact," but Tyler Wigg-Stevenson of the World Evangelical Alliance argues  that "no 'expert' can really know the future."
The problem of foretelling success is exacerbated when the purpose of the military action is unclear. What is success? Is it regime change, the protection of civilians, or deterring further use of chemical weapons by Assad and others?
Military intervention simply to punish Assad for the use of chemical weapons wins few advocates. Christiansen sees no purpose in "a feckless punitive attack with no strategic gain," though he believes the continued use of chemical weapons would require a response.
Likewise, Bacevich asks what we expect to accomplish with a very limited attack "beyond allowing ourselves to feel virtuous because we have done something in response to a reprehensible act." If "we really are morally obligated to do something, then it ought to be something more than just a gesture."
But attempting regime change or the protection of innocents also raises issues. David O'Brien of Holy Cross College believes  "U.S. intervention in Syria, carried out with the support of NATO and regional allies like Turkey and Saudi Arabia may temporarily relieve suffering but is unlikely to bring about a cease-fire, much less regional stability or sufficient safety to allow families to meet their daily needs or for refugees to return home."
Winright worries that intervention will make matters worse: "There are already over 1.7 million Syrian refugees, making a huge impact on neighboring countries such as Jordan, Turkey, and Lebanon," he writes. "I worry that military intervention at this time will only increase the suffering, especially for the civilians of Syria."
Likewise, Shadle fears "the widening of the war through the more aggressive intervention of other powers such as Russia or Iran, or the coming to power of an Islamist regime in part of or the whole of Syria if we successfully topple Assad."
Love also worries about what would follow Assad. The Obama administration "attends to the tactics of war, but not the strategies of peace," she writes. "They weigh tactical, operational questions of military logistics, basing, and targeting, the how-to of military destruction. But what sort of peace do we seek in Syria? If a U.S. military intervention helped topple Assad, who would govern the country and how?" Nor do the ethicists see any plans to reconstruct Syria after the war is over, which they say has to be part of any intervention.
On the other hand, others caution against inaction. Galston says, "We do not know whether the options we now have will prove effective, but that uncertainty does not justify doing nothing." Likewise, Qamar-ul Huda of the U.S. Institute of Peace believes  no action by the international community "can increase civilian suffering and validate the actions of an abusive government."
Galston argues: "If we can act effectively to protect innocent human life, we have an obligation to do so -- unless the costs to us are prohibitive (and there's no reason to suppose they must be). We failed that test in Rwanda but met it in the Balkans."
While Winright agrees that "the intervention in Kosovo may have been morally if not legally justified," he says "military action against Syrian forces would not at this time be morally justified." He says, "a cruise missile attack does not really seem to be what the R2P doctrine has in mind under the prong 'the responsibility to react,' which is not meant only to include military responses." He also notes that even in the Balkans war, unethical means were used, as when "NATO's desire to avoid combat casualties led to carrying out aerial bombings from higher altitudes, thereby lessening NATO's ability to avoid harming the very people they were trying to protect." He believes that "NATO bombs initially caused the Serbian army to step up its attacks on Kosovars and increased the number of refugees." He fears the same in Syria.
If the cause is just and success is probable, who has the right to intervene? Hauerwas mocks the idea of the United States acting as the world's policeman. Likewise, Wigg-Stevenson says, "the United States is not the sword of God."
Shadle argues that the decision to use force resides only in the U.N. Security Council, though Love notes "restricting right authority to the UN Security Council raises the bar for intervention in a way that is difficult to reach."
Christiansen agrees. The Russian veto "may mean resorting to the U.N. General Assembly, as was done in the case of the Korean War, or setting a time limit on a veto, or granting permission for ad-hoc alliances to act after certain thresholds of violence have been met."
But Ahern says "intervention without the clear authority of an international institution fails both the moral and legal test." It is "the responsibility of the broader community and not any one state or coalition of states to protect the people. Given its limited mandate and poor track record, I would point out that NATO is hardly a legitimate authority in this case." Despite its limitations, the UN Security Council is the appropriate body, he writes. "Any intervention that circumvents this structure only serves to weaken the ability of the international community to respond to humanitarian issues."
What comes through from these moralists is sense of frustration. Winright concludes, "No one seems innocent in this current conflict -- except for the children. I wish there was some way to take their side, on all sides." Ahern agrees.
"We know what is right, but not the course of action to bring about the right," Wigg-Stevenson says. "All we have is a set of convictions against which we can weigh a host of imperfect proposals."
Likewise, Christiansen bemoans  the fact that "the international community has come to no workable way, not just to stop the war, but specifically to prevent the Assad government's attacks on civilians. The Responsibility to Protect has become a dead letter in Syria." The ethicists also complain that little or no attention is given to preventing conflicts before they start.
Like policymakers, moralists are appalled by what is happening in Syria but are just as unhappy about the options available.
Religious leaders have also condemned the Syrian carnage and called for increased diplomatic efforts. Pope Francis demanded  an end to the fighting and denounced the "multiplication of massacres and atrocious acts."
"It is not clashes, but an ability to meet and to dialogue that offers prospects for a hope of resolving the problems," the pope said. In speaking with Jordanian King Abdullah II, Francis noted that dialogue and negotiations are "the only option for putting an end to the conflict and violence." In an unusual move, Pope Francis has called for a day of fasting for peace on Saturday.
Vatican diplomats cautioned  against a "rush to judgment without sufficient evidence." Archbishop Silvano Tomasi, the Vatican observer at U.N. agencies in Geneva, urged an internationally sponsored meeting "where representatives of all parts of Syrian society can be present, explain their thinking and try to create some kind of transitional government." The Vatican nuncio to Syria said the Syrian people are fed up. "They are crying out to the international community to say, 'Help us so that this war would end immediately. We have had enough; we can't take it anymore. We can't continue like this.' "
Bishop Richard Pates of Des Moines, Iowa, chairman of the U.S. bishops' Committee on International Justice and Peace, echoed the pope's words. "The longstanding position of our Conference of Bishops is that the Syrian people urgently need a political solution that ends the fighting and creates a future for all Syrians, one that respects human rights and religious freedom," Pates said. "We ask the United States to work with other governments to obtain a ceasefire, initiate serious negotiations, provide impartial and neutral humanitarian assistance, and encourage building an inclusive society in Syria that protects the rights of all its citizens, including Christians and other minorities."
Neither the Vatican nor the American bishops mention military intervention, but they clearly do not endorse it. Other Catholic prelates publicly oppose intervention.
The head of the German bishops' commission for international church affairs, Archbishop Ludwig Schick of Bamberg, told the Catholic news agency KNA that an armed intervention could not be justified in Catholic teaching, which required "total certainty of the confirmed damage," as well as "serious chance of success" and a capacity to avoid "worse damage than that to be eliminated." The head of the Anglican Communion, Archbishop Justin Welby of Canterbury, also spoke against military strikes.
Catholic prelates in the Middle East have been adamant in their opposition to military intervention. Chaldean Catholic Bishop Antoine Audo of Aleppo said  it "would lead to a world war." Likewise, Syrian-born Melkite Catholic Patriarch Gregoire III Laham warned against intervention  and expressed disappointment that the U.S. had postponed meeting with Russia to prepare a peace conference on Syria.
Latin Patriarch Fouad Twal also opposed intervention: "Our friends in the West and the United States have not been attacked by Syria," he said. "With what legitimacy do they dare attack a country? Who appointed them as 'policemen of democracy' in the Middle East?"
Archbishop Maroun Lahham, patriarchal vicar for Jordan in the Latin Patriarchate of Jerusalem, also opposed intervention and said that no one in the Middle East would believe that the United States was intervening to defend the weak.
While opposing military intervention, these religious leaders would welcome humanitarian aid to Syrian refugees.