Juxtaposed articles in Monday's New York Times concerned two incidents, widely separated in space and time, in which civilians died in military operations. In one, an Israeli panel released the conclusions of its inquiry into an airstrike in Gaza in 2002 which Israel used to kill a senior member of Hamas. The target was in a densely populated neighborhood, and the strike caused several buildings to collapse, killing at least 13 civilians, most of them women and children. The other article concerned an Afghan investigation into an incident two weeks ago in Kunar Province in which NATO airstrikes killed civilians—as many as 65 of them, according to the Afghan investigators.

Civilian casualties in warfare have long been a moral, political, and legal issue, of course, but many of the ambiguous circumstances in which military forces operate today seem to raise this disturbing topic with increasing frequency. The circumstances vary greatly. The NATO forces in the recent incident in Afghanistan were conducting air operations against Taliban elements in an insurgent-controlled area. The Israeli strike in Gaza was intended to take out a Hamas figure whom the Israelis were convinced had been directly involved in planning terrorist attacks that had killed Israeli civilians. In one of the deadliest incidents of civilian collateral deaths that involved the United States—the accidental shooting down of an Iranian airliner over the Persian Gulf in 1988, in which 290 persons died—the U.S. cruiser that fired the missile was in the Gulf to protect neutral shipping during the last months of the Iran-Iraq War. Currently in northwest Pakistan almost every week a U.S. drone fires a missile at a suspected militant; many of these missile strikes have also claimed other lives, with some of the collateral damage becoming matters of controversy. What is one to make of such incidents? What are the standards for judging what is justified from what is not? The diverse circumstances tax the limits of applicability of what moral philosophers have offered regarding just and unjust ways to fight wars.

There is a tendency for opinions about the rightness or wrongness of specific actions to track with opinions about the larger campaigns of which they are a part. Many people will evaluate the incidents in Afghanistan and Gaza according to their evaluations of the worth and advisability of NATO's overall campaign in Afghanistan or of Israel's overall use of force against Hamas. That tendency should be resisted. The legitimacy of any specific armed action is a different question from the legitimacy of an entire war, although the two questions may be related.

We also need to be mindful of the factual uncertainties that typically surround these incidents. The NATO command disagrees with Afghan investigators' version of the events in Kunar, acknowledging that some civilians were killed but that the number is far less than asserted and that many of the casualties counted as civilians were in fact insurgents. Major factual disagreement persists to this day over the incident in the Persian Gulf involving the Iranian airliner, with many and probably most Iranians believing that the shooting was intentional rather than a tragic case of mistaken identity by the nervous crew of a warship.

Commanders and political leaders who decide on the use of force also typically face major information gaps and uncertainties when they make their decisions—about who is an insurgent and who is a noncombatant, for example, or about how many other people are in a house along with the intended target. One of the principles that decision-makers should keep in mind is that their information is incomplete and may in some respects be wrong. Launching a military operation while being cocksure of the situation one faces is not a moral way to employ armed force.

Beyond informational modesty, there are some criteria to consider when contemplating the use of force that may entail civilian casualties—but they are only criteria, not any hard and fast formula for making the decision. One is the value of accomplishing whatever one hopes to accomplish with the use of force. Another is the likelihood of accomplishing it. And another is the likelihood of harming innocent civilians. Comparing that likelihood with the importance of what the use of force will achieve introduces the concept of proportionality. The Israeli inquiry, which was headed by a retired supreme court justice, determined that the civilian casualties from the airstrike in Gaza were “disproportionate”. This judgment is significant; the Israeli government eschews the term “disproportionate” because the collateral damage from many Israeli military operations has been, well, disproportionate. (The outstanding recent example is Operation Cast Lead, the invasion of the Gaza Strip in 2008-2009 in which more than a thousand Palestinians died, a large proportion of them noncombatant civilians.)

Underlying the concept of proportionality is the moral principle of valuing all human life, not just life of a particular nationality. Difficult issues arise in warfare because every nation naturally gives first priority to the safety of its own citizens, civilian or military. But an attitude that says anything goes to protect one's own people, with little or no regard for the safety of other people, is an attitude divorced from morality and as such is indefensible.