Read: When do we get to call someone a terrorist?

The NCTC’s mandate is to focus on acts with some connection, even if it’s only ideological, to a designated foreign terrorist organization; this is what the NCTC spokesperson was referring to. But whether it’s international or domestic, there are hundreds of definitions of terrorism in scholarship and common usage.

Some require the targeting of civilians; others don’t. Some require it be committed by non-state actors, while others allow for the possibility of “state terrorism.” Terrorism’s modern connotation is one of illegitimate and indiscriminate violence, but in 1794, Robespierre defined it in glowing terms: “Terror is nothing less than immediate justice, severe, inflexible.”

Within U.S. law alone, Nicholas J. Perry, a lawyer at the Department of Homeland Security, has found more than 22 definitions or descriptions of terrorism.

The one common feature of most definitions of terrorism today is that it requires a political motive.

New York Governor Andrew Cuomo had it partly right in a press conference Wednesday. Cuomo said that the intent of terror was to terrorize, and the pipe-bomb mailings were clearly intended to terrorize, ergo, they must be terrorism. But there are many other kinds of violence—from mass shootings to domestic abuse—that terrorize without quite being terrorism.

Read: The difference between a killer and a terrorist

The political motive looked clear to anyone observing the pattern of the pipe-bomb mailings this week. After all, they weren’t just targeting random public figures, but specific ones who happened to be prominent Trump critics.

But what if the attacker was mentally disturbed in some way?

The anthrax mailings of 2001 appeared to have an obvious, if confusing, political motive. Those letters were mailed to media and Democratic figures, accompanied by notes saying “Death to America. Death to Israel. Allah is great.” As investigators closed in on the civilian Army microbiologist Bruce Ivins, who killed himself in 2008 before being charged, the picture became more complicated with reports that he had suffered from severe mental illness. This raised the question: Was his goal in sending a bioweapon through the mail really to coerce a political outcome? Or was it the product of some delusion?

Read: Today’s terrorists want to inspire

The Orlando nightclub shooting, in which Omar Mateen shot and killed 49 people in an attack claimed by ISIS, raised similar questions. The shooter, who was killed by police, had also reportedly suffered from mental-health problems. Could ISIS really credibly claim the actions of a disturbed man as their own?

These examples illuminate the larger point: “Terrorism” is fundamentally about motivation, which is often unknowable.

As the terrorism scholar Martha Crenshaw told me in 2015, you could look at the same crime—say, the assassination of a political figure—and your categorization of it would change depending purely on what was in the attacker’s mind. Did he want to overthrow the regime? Or was he nursing a long-standing grudge from knowing the political figure during his school days?

Terrorism in one case, crime in the other, far-reaching consequences regardless.