During a press conference in San Bernardino on Thursday, law-enforcement officials noted that the two dead suspects in Wednesday’s massacre had stockpiled an enormous arsenal: thousands of rounds of ammunition, 12 pipe bombs, and material to build more. They said that the couple, Syed Rizwan Farook and Tashfeen Malik, seemed to be preparing for more carnage in separate attacks. They noted “international travel,” and said that “if you look at the amount of obvious preplanning … there was obviously a mission here.” Anonymous officials told various news organizations that they believed the couple was in touch with suspected terrorists.

But when a reporter asked David Bowdich, who heads the Los Angeles field office of the FBI, whether the attack was terrorism, he was careful not to make a ruling.

“It would be irresponsible and premature for me to call this terrorism,” Bowdich said. “The FBI defines terrorism very specifically, and that is the big question for us, what is the motivation for this.”

This is a debate that plays out nearly every time there’s an act of mass violence. Sometimes, it’s a matter of legal proceedings—deciding what laws apply in charging suspects. That’s less important here, since both of the alleged attackers are dead, but the issue has become politically contentious. So how does the FBI define terror?

“Domestic terrorism” means activities with the following three characteristics:

  • Involve acts dangerous to human life that violate federal or state law;
  • Appear intended (i) to intimidate or coerce a civilian population; (ii) to influence the policy of a government by intimidation or coercion; or (iii) to affect the conduct of a government by mass destruction, assassination, or kidnapping; and
  • Occur primarily within the territorial jurisdiction of the U.S.

The definition for international terrorism is basically the same, except that it involves activities “outside the territorial jurisdiction of the U.S., or transcend national boundaries.” The “federal crime of terrorism” includes acts “calculated to influence or affect the conduct of government by intimidation or coercion, or to retaliate against government conduct.”

No wonder Bowdich didn’t yet feel comfortable asserting that the attack had the political intent stipulated in the law: to intimidate or coerce civilians, or to influence the government. “It’s way too early to speculate on motive,” he said. In particular, investigators are struggling to understand why, with many pieces of evidence pointing toward radical Islamism, Farook and Malik chose the target they did. They attacked Farook’s employee holiday party—a choice with the hallmarks of a workplace shooting. (Bowdich wondered aloud during Thursday’s press conference whether the couple were planning an attack and then decided for some reason to target the gathering.) The specificity of the legal definition may also explain explain Obama’s reticence during a statement Thursday morning, when he said: “It is possible that this was terrorist-related, but we don’t know.”

But the disconnect between the strict legal definition of terrorism and what the general public sees as terrorism creates some difficulty. In the case of an attack like September 11, it’s an easy call. Beyond that, things get muddy. Throw in academic definitions and the matter gets even muddier. “It’s just kind of hard empirically to get at what we mean by terrorism—violence that’s symbolic, violence that’s meant to communicate, to send a message—how, just objectively, do you distinguish that from any other sort of violence?” Martha Crenshaw told my colleague Kathy Gilsinan in September.

After major acts of violence, there’s often a chorus that insists that the terror label be quickly applied, but the makeup of that chorus is often very different.

“We are deeply concerned that this is yet another manifestation of terrorism—radical Islamic terrorism here at home,” Senator Ted Cruz told the Republican Jewish Coalition Thursday morning, where the GOP presidential candidates were speaking. “Coming on the wake of the terror attack in Paris, this horrific murder underscores that we are at a time of war, whether or not the current administration realizes it or is willing to acknowledge it.” Others also took Obama to task for not invoking the T-word in cases involving alleged or proven Islamist ties.

On the other side of the aisle, progressives have been eager to apply the label of terrorism to non-Muslim violence. There were calls to label Colorado Springs Planned Parenthood shooter Robert Dear and other abortion-clinic attackers as terrorists. (Republican presidential candidate Mike Huckabee notably agreed, calling the shooting “domestic terrorism.”) Other writers have made the case that police violence against people of color fits the definition of terrorism, because it is violence aimed at affecting the behavior of a group of people.

It’s easy to say that the FBI’s definition doesn’t matter, that it’s just a matter of semantics, but that ignores the very reasons that people outside of justice system demand the label. Once something is a officially deemed an act of terror, it holds greater meaning. It changes an event from senseless violence to part of a larger landscape. It delivers a larger culprit, a target that is, if not easier to beat or to understand, at least identifiable.

As it regards San Bernardino, the desire to label the attack terrorism seems to fall into the middle of a partisan debate. Gun-control-favoring progressives want to group this with other mass shootings, as evidence that U.S. firearm regulation need tightening. Gun-friendly conservatives would rather talk about Islamic radicalism, preferring to discuss the threat of terror. In reality, of course, these debates aren’t as mutually exclusive as some might like. It’s possible for people carrying out attacks inspired by Islamic radicalism to exploit the constitutional right to bear arms, and America’s comparatively permissive gun regulations. (On Tuesday, in fact, a measure that would have prevented people on the terrorism watch list from buying guns was defeated in the House of Representatives.)

Amid these debates, the FBI has remained consistently very cautious and slow about what it calls terror. After an apparently radicalized gunman opened fire at a military-recruitment center in Chattanooga, Tennessee, this summer, the Times Free Press notes, a U.S. attorney called it “domestic terrorism.” The next day, he gingerly backed off, noting that the FBI had deemed it only a “terrorism investigation.”

The same happened after the massacre at Emanuel A.M.E. Church in Charleston, South Carolina. In that case, alleged shooter Dylann Roof even told friends he wanted to start a race war. “There is a word for premeditated violence against civilians by non-state actors who intend to stoke fear, anger, and social strife in service of their extremist ideology,” my colleague Conor Friedersdorf wrote. “That word is terrorism.”

But when FBI Director James Comey was asked about it two days after the June shooting, he wouldn’t agree. “Terrorism is act of violence done or threatens to in order to try to influence a public body or citizenry, so it’s more of a political act and again based on what I know so more I don’t see it as a political act,” Comey said.

The following month, The Huffington Post asked him again. “I don’t know yet,” he said. “I was asked about that a day or so after and said that, based on what I knew at that point, I didn’t see it fitting the definition. Since then, we’ve found the so-called manifesto online, so I know the investigators and prosecutors are looking at it through the lens of hate crime, through the lens, potentially, of terrorism.”

Besides, Comey added, whether he called it terrorism “doesn’t impact the energy that we apply to it.”