A pair of U.S. Air Force F-15E Strike Eagles fly over northern Iraq after conducting airstrikes in Syria on Sept. 23. (Us Air Force/Reuters)

When is a war not a war? Does it matter, when a bomb is dropped or a missile launched, whether it’s called “counterterrorism,” or “armed conflict,” or “hostilities”?

Actually, it does — especially to a president who has said he wants to keep American military action within the bounds of U.S. and international law, and to administration officials who have spent countless hours in recent weeks parsing the language used to describe operations in Syria.

It matters to the American people, who have said in surveys that they favor airstrikes against Islamic State militants in both Syria and Iraq but aren’t much interested in fighting another Middle East ground war. It also matters to Congress, which has not authorized a war since World War II but may decide to approve this specific “use of military force.”

For civilians on the ground, the likelihood of being hit by a U.S. airstrike may be different under President Obama’s narrow guidelines for non-war counterterrorism than under broader international rules governing “armed conflict.” And European allies, several of which have joined U.S. air operations in Iraq, remain uncertain of the international legal justification for military action in Syria.

The administration’s definition of what it is doing has continued to evolve in recent weeks. As government lawyers struggle to provide the president with maximum flexibility under both domestic and international law, the results at times have seemed both inconsistent and confusing.

When Obama announced on Sept. 10 that he had authorized offensive U.S. military action, he emphasized the potential threat the Islamic State posed to the U.S. homeland and said his objective was to “degrade and ultimately destroy” the group. Neither the president nor White House briefers who provided additional context for his remarks mentioned a request by the government of Iraq to conduct airstrikes in Syria.

Yet that request is now cited as a key international legal underpinning for the strikes that began on Sept. 22. It is not clear when it was initially made. On Sept. 23, U.S. Ambassador to the United Nations Samantha Power referred to an Iraqi letter sent to the U.N. secretary general three days earlier reporting an appeal to the United States to “lead international efforts to strike ISIL sites and military strongholds in Syria in order to end the continuing attacks on Iraq.”

Power cited the U.N. Charter’s recognition of the legitimacy of using force for both individual and collective self-defense. She did not mention the objective of destroying the Islamic State, also known as ISIL and ISIS.

The day after Obama’s nationwide address, CNN asked Secretary of State John F. Kerry whether the United States was at war with the Islamic State. That was the “wrong terminology,” Kerry said. “What we are doing is engaging in a very significant counterterrorism operation.”

Three days later, on CBS’s “Face the Nation,” Kerry called such semantic debates “a waste of time.” But, he said, “If people need a place to land . . . yes, we’re at war with ISIL.”

Obama, who has said in the past that the United States is “at war with al-Qaeda,” seemed to disagree when asked the war question about the Islamic State on CBS’s “60 Minutes” on Sept. 28.

“This is not America against ISIL,” he said. “This is America leading the international community to assist a country [Iraq] with whom we have a security partnership with, to make sure that they are able to take care of their business.”

When reporters asked the Pentagon press secretary, Rear Adm. John F. Kirby, on Tuesday whether the U.S. military was “at war with ISIL,” his response was succinct. “Yes, yes,” Kirby said.

Administration lawyers, seeking outside advice, have discussed the Iraq and Syria operations with a number of former officials. “We have encouraged them . . . to clarify publicly their legal theories under both domestic and international law,” said a participant in some of those closed-door discussions who would only discuss a private meeting on the condition of anonymity.

‘Armed conflict’ vs. ‘war’

International law, which uses the words “armed conflict” instead of “war,” applies whether states are fighting each other or against “non-state actors,” such as terrorist groups, although terrorists by definition do not follow the rules.

The law recognizes the possibility of civilian casualties. But governments cannot intentionally target civilians, and any action putting civilians at risk must be proportionate to the importance of the military objective.

In guidelines for lethal counterterrorism action he outlined last year, Obama imposed the narrower standard of “near certainty” that there would be no civilian casualties. But “that was then and this is now,” said John B. Bellinger III, State Department legal counsel in the George W. Bush administration. “I mean that seriously. When they were coming up with all those rules a year ago, they thought the terrorist threat was heading in one direction. Now it seems to be a completely different direction.”

Amid reports of civilian casualties from U.S. strikes in Syria — which the Pentagon said it had not confirmed — administration officials said the “near certainty” standard applied only “outside areas of active hostilities,” based on “among other things, the scope and intensity of the fighting,” said a senior administration official who spoke on the condition of anonymity about legal conclusions.

“We consider Iraq and Syria to be ‘areas of active hostilities,’ based on what we are seeing on the ground right now,” the official said. “This is not the same as a determination that an armed conflict is taking place in the country at issue.” Nevertheless, the official said, the administration has chosen to comply with laws applicable to armed conflict where possible civilian casualties are concerned.

But “in international law, there is only one concept — an armed conflict, or not,” said one former senior administration official who spoke on the condition of anonymity to candidly describe the administration’s quandary. The United States, the former official said, now recognizes something in between — a new category of “a hot battlefield, or an area of active hostilities.”

The administration has also said its actions are a legal response to the threat because Syria is “unwilling or unable” to fight the Islamic State itself. Naz Modirzadeh, founding director of the Harvard Law School Program on International Law and Armed Conflict, called that concept an example of “folk international law.”

Established law, she wrote Thursday on the Lawfare blog, includes no such distinction for violations of sovereignty.

The role of Congress

Under the Vietnam-era War Powers Resolution, the president must notify Congress whenever he sends U.S. forces into “hostilities” and must withdraw them after 60 days unless lawmakers agree.

Obama observed the requirement when launching U.S. military operations in Libya in the spring of 2011 but then adopted what critics called an elastic definition in deciding that the situation did not constitute “hostilities” that put U.S. military personnel at risk, and thus was not subject to the deadline.

In Iraq and Syria, Obama sent the notifications but has said he does not need congressional approval, because U.S. actions are separately justified by the president’s constitutional authority as commander in chief and the 2001 Authorization for Use of Military Force (AUMF) against al-Qaeda and its associates.

Last year, Obama proposed narrowing, and ultimately repealing, the al-Qaeda measure as outdated in an era in which that organization’s core leadership had been “decimated” and new, independent terrorist threats were emerging. Although he pledged to consult Congress on new authorizations for new threats, and some legislation was proposed, nothing had happened by the time the Islamic State took over vast territory in both Syria and Iraq.

The Islamic State and al-Qaeda have mutually and publicly rejected any association with each other. But the administration has said the once-rejected AUMF is valid, because the Islamic State is rooted in an al-Qaeda-linked group born in Iraq a decade ago.