When French President François Hollande declared that the deadly attacks against Paris were an "act of war," former Conservative defence minister Jason Kenney tweeted that this declaration "has implications for Canada under the NATO Treaty's Article 5."

Kenney was referring to an article of the 1949 North Atlantic Treaty, which formed the foundation of the North American and European alliance.

According to Article 5, an attack on one NATO member is considered an attack against them all. And it calls on the alliance members to assist the attacked country by taking "such action as it deems necessary, including the use of armed force."

In practical terms, however, the 28 NATO members, including Canada, would have no obligation to take any action.

"If Article 5 is invoked, it actually formally does not require Canada to do anything," said Stephen Saideman, the Paterson Chair in International Affairs at Carleton University. "Canada can choose to do as little or as much as it wants."

"What it means ultimately is that Article 5 requires nothing from anybody. Every country can react as they see fit. Countries don't have to participate."

'A clarion call'

So if Trudeau is still set on withdrawing the CF-18s currently involved in the air bombing mission against ISIS in Iraq and Syria, Canada's obligations to NATO would have no bearing on his decision.

"Article 5 is a clarion call to draw attention and confirm solidarity, while the actual response might be much more uneven as a result of negotiation among NATO members," said Robert Baines, a corporate development officer for the NATO Association of Canada.

"While Canada would not be obligated to take any specific action, there would be larger considerations of international relations with our NATO allies, and I'm sure we'd have to make some meaningful contributions to an Article 5 response," said Baines.

NATO Secretary General Jens Stoltenberg, from Norway, right, is greeted by French President François Hollande prior to their meeting at the Elysée Palace in Paris in March 2015. (Remy de la Mauviniere/Associated Press) NATO is not just a military alliance, but also a political and diplomatic one, Baines said. Country representatives meet regularly in order to confirm support for their particular positions.

"Canada would be under a certain amount of pressure to participate meaningfully in a response to the attack, but there is no compulsion regarding how we respond."

Whether Article 5 will be invoked is still an open question. The only time it has been used is after the Sept. 11, 2001, attacks.

France would first have to request an Article 4 consultation. And it would be the North Atlantic Council, after consultations with representatives of the 28-member alliance, that would decide whether to invoke Article 5.

"Many bilateral and joint meetings among NATO members would be undertaken to negotiate the response before a united front would be displayed as an alliance," said Baines. "When Article 5 was invoked on Sept. 12, 2001, it took almost a month to confirm the source of the attack and the response."

EU mutual defence clause

This week, France invoked the mutual defence clause of the European Union treaty, the first time a member country has done so. It too states that if a member state is attacked, other members are obliged to aid and assist. But much like Article 5, it doesn't require military assistance.

A reluctance by France to call for NATO's help would not be altogether surprising, as the country has a long history of ambivalence toward the organization, Saideman said.

From the mid-1960s, then president Charles De Gaulle wanted France to forge an independent foreign policy and pulled out of NATO's operational chain of command. While that changed under president Nicolas Sarkozy, who wanted France to play a larger role in NATO, it's unclear whether Hollande wants France to return to its traditional relationship with NATO.

The main value of Article 5 would be to rally support and solidarity, and France already has that, said Baines, who doubts France would seek out NATO to respond to the attacks.

"Many aspects of a NATO response have already begun to be made through pledges of military, intelligence and logistical support. Any augmented campaign in Iraq and Syria will almost certainly have to work in conjunction with Russian forces, and NATO involvement might not be the best option for that to work."

If France intended to invoke Article 5, those moves would have been foreshadowed immediately, said Adam Chapnick, professor of defence studies at the Canadian Forces College. After the Sept. 11 attacks, the Americans made it clear quickly that they intended to make the attacks an Article 5 issue.

Urgency passing

"France has had many opportunities to do that. They haven't yet," he said. "They didn't do it when the situation was most urgent, which makes it less likely that they would do so now, nor has any other NATO member suggested this should be done."

"There have been pundits who have suggested [they do] so. But I haven't seen any official head of government or official head of state come out and say we need to activate Article 5 here."

As well, framing the French response as a NATO response potentially gives other states an excuse to do less, Chapnick said.

"If the Russians decided all of a sudden this is a problem, we don't want to be involved anymore, they have the out to say this is a NATO issue, not a global issue," said Chapnick.

"I think it's in the West's interests and France's interest to portray ISIS as having attacked the world. If it's only attacked NATO, that takes a lot of potential allies out of the picture. I don't see what benefit you gain from framing this as a NATO problem rather than a global problem."