On Thursday in Washington, as my colleague David Johnston reports, several legislators declared at a Senate hearing that the murder of 12 soldiers and a retired guardsman at Fort Hood this month was “a terrorist attack.” Senator Joseph I. Lieberman, who opened the hearing, said, “We will look at the Fort Hood murders not as an isolated event, but as part of a larger pattern of homegrown terrorism that has emerged over the past several years.”

Given that it is obviously important to some people to call this atrocity an act of terrorism, it seems worth asking both if most people can agree on what the word means and why it matters what we call such brutal acts.

To deal with the first question, while there have long been debates in journalism about when it is appropriate to describe politically motivated atrocities as acts of terrorism, most discussions of what is and is not a terrorist act seem to focus on attacks carried out against civilians. (In 2008 our public editor, Clark Hoyt, looked at how The Times uses the term; in January the executive editor, Bill Keller, responded to reader questions on the subject.) That raises the question of whether an attack on soldiers, like the rampage at Fort Hood, can be called an act of terrorism.

In 2002, the political philosopher Michael Walzer — who once said, “Terrorism flourishes in part because there are so many people in many parts of the world who are prepared to make excuses” — tried to define the term in his essay, “After 9/11: Five Questions About Terrorism.” In response to the first of those questions, “What is it?,” Mr. Walzer wrote:

It’s not hard to recognize; we can safely avoid postmodernist arguments about knowledge and truth. Terrorism is the deliberate killing of innocent people, at random, in order to spread fear through a whole population and force the hand of its political leaders. But this is a definition that best fits the terrorism of a national liberation movement (the Irish Republican Army, the Algerian National Liberation Front [F.L.N.], the Palestine Liberation Organization, the Basque Separatist Movement, and so on). There is also state terrorism, commonly used by authoritarian and totalitarian governments against their own people, to spread fear and make political opposition impossible: the Argentine “disappearances” are a useful example. And, finally, there is war terrorism: the effort to kill civilians in such large numbers that their government is forced to surrender. Hiroshima seems to me the classic case. The common element is the targeting of people who are, in both military and political senses, noncombatants: not soldiers, not public officials, just ordinary people. And they aren’t killed incidentally in the course of actions aimed elsewhere; they are killed intentionally. I don’t accept the notion that “one man’s terrorist is another man’s freedom fighter.” […] In the 1960s, when someone from the F.L.N. put a bomb in a cafe where French teenagers gathered to flirt and dance and called himself a freedom fighter, only fools were fooled. There were a lot of fools back then, and back then — in the ’60s and ’70s — was when the culture of excuse and apology was born.

In an interview in 2006, Mr. Walzer was asked if it was ever possible for attacks on soldiers to be acts of terrorism. He answered:

My instinct is to say that attacks on soldiers are not terrorist attacks. That does not make them right, terrorism is not the only negative moral term in our vocabulary. I did not think that the plane that flew into the Pentagon in 2001 was a terrorist attack or, better said, it was a terrorist attack only because the people in the plane were innocent civilians who were being used and murdered. But if you imagine an attack on the Pentagon without those innocent people in the plane, that would not have been a terrorist attack — whereas the attack on the Twin Towers was terroristic. I feel the same way in the Israeli cases: whatever you want to say about Palestinian resistance to the occupation, there is a difference between attacking soldiers and killing civilians, and it is an important moral difference. Now there are ambiguous cases. In the film “The Sorrow and the Pity” — Marcel Ophül’s movie about the German occupation of France — there is a wonderfully complicated moment when, after the French have surrendered, Vichy has been created, the Germans are in the North, and there is a column of German soldiers marching on a French country road. Their guns are not “at the ready,” just on their backs, and they march past a group of peasants working in the fields; but these are not really peasants, and as the soldiers march past, the “peasants” attack them. It is the example I bring [up] in my “Just and Unjust Wars.” Now the Germans said, this is terrorism. And you can make that case because the French had surrendered, the German soldiers were no longer fighting men; they thought they were in a safe place; that is why they were not moving more cautiously through the countryside. But still, an attack on soldiers is different from an attack on civilians — and there were German civilians and even families in Paris and other cities, and the French resistance did not try to kill them. So I would work very hard to maintain that distinction.

While there are important differences between the soldiers killed at Fort Hood and the examples Mr. Walzer cited — they were filling out forms at a readiness center in Texas before deploying to Iraq or Afghanistan, and they were killed by a member of their own army — it is obviously true that soldiers getting ready to go to a war zone are not civilians or noncombatants.

That doesn’t make their cold-blooded murders any less horrible, but as Americans continue to try to make sense of terrorism in the years after the Sept. 11, 2001, terrorist attacks, which were carried out by people who insisted on erasing the line between combatants and civilians, it seems plausible to ask if we want to erase that line ourselves.

Another way of asking this question is to compare the situation at Fort Hood to the attack on the U.S.S. Cole that killed 17 American sailors in Yemen, far from what they thought was any battlefield. Was that a terrorist attack or an act of war? What about the 1983 bombing of a barracks in Beirut that killed 220 marines, serving as peacekeepers? Are there any differences that matter, or is the killing of anyone, civilian or soldier, not on a battlefield an act of terrorism?

One last question before turning this over to readers: does it ever matter what the intentions of the attackers are? If the Cole bombing was carried out by a Qaeda operative and the Beirut bombing by members of Hezbollah, does that make them terrorist attacks, even though they were carried out against military personnel?

To return to the case of Fort Hood, it has been reported that the accused gunman, Maj. Nidal Hasan, may have cracked under a tangle of psychological pressures, some perhaps related to his personal fears, others that might be traced to his political or religious beliefs.

A cousin said that Major Hasan was upset about being deployed to work with fellow soldiers in Afghanistan and told family members that he had heard horrible things from his patients about war. During his training, he made a presentation to colleagues about the problems Muslim soldiers might have with fighting fellow Muslims, but he also received a negative evaluation that listed among his problems not just inappropriately discussing religion with his patients but also having poor test scores, not seeing enough patients and being overweight.

He also reportedly exchanged e-mail messages with a radical cleric in Yemen who seems to have inspired others to plan terrorist attacks, but counterterrorism investigators saw no reason for alarm after reading those notes well before the attack. The cleric has reportedly denied encouraging Maj. Hasan to take up arms.

Several witnesses to the rampage said they heard Maj. Hasan shout “Allahu Akbar,” or “God is Great,” before the shooting, but, as William Langewiesche explained in his examination of the crash, in 1999, of Egypt Air Flight 990, investigators from the National Transportation Safety Board learned that invoking god can have lots of different meanings and many Muslims use the word “Allah” at times of stress who are not radical jihadists. The Lede, like many news organizations, has also reported that the very same phrase, “Allahu Akbar,” has been shouted from rooftops by reformers in Iran who are using it to express their passionate opposition to the Islamist government there.

Finally, to readers who believe that it is important to call the attacks at Fort Hood, and possibly the killing of other soldiers in other situations, “terrorism,” we would be glad to hear from you why you believe that the use of that word is important. Can making this designation somehow help us to prevent such attacks, as Mr. Lieberman suggested on Thursday in the Senate, or is it useful in some other way?