War is hell. Just ask any soldier who has fought a battle, and he will tell you a war might be just, but it’s never good.

“Just” but not “good” seems to be a contradiction, and even youngsters try to make sense of it. One day a young boy asked his father, “Dad, if everyone knows that wars are bad, why do they have them?”

“Why, indeed?” the father thought to himself. And yet the fact of war is as old as the human race. It dates back to that first mortal act of aggression by Cain against Abel.

Just War Doctrine

Great minds have wrestled with the morality of war in every age, because war has seemed both unavoidable and at the same time reprehensible. Over the centuries the Church has developed doctrine about the criteria for determining whether a war is just or unjust.

This “just war doctrine” attempts to balance the rights of victims against the social benefits of peace and stability in order to serve the common good. In all cases, people agree that war should be a last resort to vindicate rights.

How did just war doctrine develop? Even before the time of Jesus Christ, great thinkers urged limits on war and offered rules of engagement.

In classical antiquity, the Greek philosophers Plato (c. 428-c. 348 B.C.) and Aristotle (384-322 B.C.) argued that war is reasonable only in order to re-establish peace. Cicero (106-43 B.C.), the renowned Roman statesman and jurist, went further and established three rules for war: 1) just cause; 2) declaration of war by the legitimate authority; and 3) just conduct of the war.

In the century after Cicero, Jesus Christ came preaching forgiveness and reconciliation in the Sermon on the Mount: “Blessed are the peacemakers” (Mt 5:9) and turn the other cheek (see Mt 5:39). Later, when St. Peter tried to defend Jesus from those who had come to take Him away by force, Jesus told the apostle to put away his sword (see Mt 26:52).

But was Jesus truly a pacifist? Some think not and have taken His words about the spiritual battle to justify armed conflict.

Our Lord said: “Do you think that I have come to establish peace on the earth? No, I tell you, but rather division” (Lk 12:51). Then later: “One who does not have a sword should sell his cloak and buy one” (Lk 22:36).

Moreover, inspired Scriptures quoting St. John the Baptist and St. Paul recognize the legitimacy of the soldier’s profession (see Rom 13:4; Lk 3:14.) If the Sacred Scriptures were our only point of reference, reasonable people might argue about whether revelation supports the just war doctrine because the Scriptures just cited seem to contradict one another.

Fortunately, we have recourse to the living Tradition and Magisterium of the Church for guidance on such important matters.

Just a few centuries after the time of Christ, St. Ambrose (340-397) adopted Cicero’s rules of war, and his student St. Augustine (354-430) would later expand on just war doctrine in a number of his works. Augustine recognized the horror of war, but understood armed conflict to be a necessity and not so much a matter of choice.

In addition to the two Ciceronian reasons that justify the right to go to war (ius ad bellum), he specified that part of conducting a war fairly (ius in bello) meant recognizing the rights of clerics to be exempt from military service.

Later, St. Thomas Aquinas would expand on this and resolve the doubts about the legitimacy of fighting on holy days and laying am-bushes. Finally, in recent times, the Church’s reflections on the horrors of world wars led an ecumenical council and several popes to plead for “war, never again!”

Principles of Just War Doctrine

The just war doctrine of the Church presumes in favor of peace and establishes a rigorous moral framework that seeks to prevent war. The justification for war is based on a right to self-defense, but self-defense must always be proportional to the act of aggression.

The difficulty with these principles, of course, is that they are necessarily broad and open to interpretation.

Let’s take a closer look at the four conditions for a just war, which must all be present at one and the same time.

First, the damage inflicted by the aggressor must be lasting, grave and certain. This statement assumes that the damage is unjust and therefore one side is right and the other side is wrong. In other words, the war can be a just action for one side, but not for the other.

This conclusion is based on the principle of noncontradiction. In reality, both sides might think they are right, but in a truly just war, only one side can be right. In fact, many times wars are unjust, and both sides are wrong.

Besides being lasting and grave, the damage must be certain. There are three levels of certainty: subjective, moral and absolute.

Some writers argue that only moral certainty about the damage inflicted is necessary. Yet moral certainty is a category more suitable for marriage-nullification cases in which it is often impossible to reach absolute certainty about the psychological capacity of a spouse.

Because of the awful consequences of war, more prudent moralists argue that absolute certainty about the damage inflicted and the identity of the aggressor must be present before launching an attack.

This first set of conditions makes it difficult to understand, for example, how a “pre-emptive strike” against a potential aggressor who threatens to use weapons of mass destruction could be justified unless there is absolute certainty the foe does indeed possess weapons of mass destruction.

Next, “all other means of putting an end to it must have been shown to be impractical or ineffective.” Again, this principle is open to interpretation. An impatient government would be inclined to attack rather than rehearse another charade of diplomacy with a wily enemy. But the point here is simply this: War is just only as a last resort.

The third principle, “there must be serious prospects of success,” largely depends on the will of the people.

Great Britain did not have much hope at the beginning of World War II, but the British were convinced they would rather die than serve Hitler’s designs. The American colonists were potentially outnumbered and poorly armed, but they were convinced that liberty was worth the fight.

The fourth and final criterion (“the use of arms must not produce evils and disorders graver than the evil to be eliminated”) is perhaps the most difficult to meet. That’s because the use of military force often incites hatred and retaliation, leading to an escalation of conflict and a downward spiral of violence and degradation.

Who Evaluates?

The question remains who has the responsibility to evaluate these conditions, to determine if a specific war is actually just. That belongs to those who have the responsibility for the common good.

In the case of the United States, such responsibility rests with our elected officials and is a matter of prudential judgment.

Normally, it’s not the responsibility of the hierarchy of the Church to judge whether a conflict is just according to these conditions, unless the circumstances are clearly contrary to the conditions for a just war. Still, it is the responsibility of the Church to teach the truth and urge people to reconciliation, mutual trust, cooperation and solidarity.

In proposing these principles, the Church stands on a higher moral ground with a longer historical vision and a deeper understanding of humanity than secular governments. If the citizens of a particular democracy are convinced that their elected officials have made an error of judgment, they have a responsibility to make their voices heard.

Father Francis Hoffman, J.C.D., is chaplain of Northridge Preparatory School in suburban Chicago and a regular contributor to Relevant Radio’s “Morning Air Program.”