‘Nous sommes en guerre.’ Nicolas Sarkozy’s statement on Sunday morning, after meeting François Hollande to discuss the massacres in Paris, echoed his successor’s statement to the French people on Friday evening, which used the g-word four times. Modern statecraft deploys a mobile army of mixed metaphors, as when the ‘they’ who kill ‘us’ are also partly ‘us’. If it’s war abroad, does that mean that Friday’s killers count as combatants, with Geneva Convention rights, and that military action needs legal authorisation? If it’s domestic terrorism, what title does the state have to range beyond its borders, pursuing Isis on foreign sovereign territory?

Isis’s stated ground for the Paris attacks is the French military strikes against it, which President Hollande extended late in September from Iraq to Isis training camps in eastern Syria. As with the US/British operation which seems to have taken out Mohamed Emwazi on Thursday, the legality question, if raised at all, is consigned to a decisionistic limbo: we ‘evaporated’ Emwazi, so what’s not to like? One thing not to like, apart from the plausible claim that these actions are self-defeating in the long run, is that it undermines the claims to moral superiority it’s premised on, and further alienates regional powers whose co-operation it needs. Islamic terrorism is a virus that constantly mutates. ‘War’ against it is not finally winnable. Failure to win calls forth a predictable spiral of outrage and misconceived response.

As far as international law goes, Western states’ unilateral or joint military action in Syria could be legalised on three grounds: a UN Security Council resolution (but that would be vetoed by Russia and China); invitation by Assad (but, unlike with Russia, that has not been forthcoming); or in defence of another state. The US and UK have invoked Iraq’s request for military assistance to justify their intervention in both Iraq and Syria. But, because Isis is not recognised as a state, this ground is problematic. In 2005, the International Court of Justice found Uganda’s intervention in the Democratic Republic of Congo against anti-Ugandan rebels to be illegal – it would have been legal only if the DRC had backed the rebels, but they were among a plethora of anti-government militias active in eastern Congo. Clearly, Assad is not backing Isis. Sovereign states’ title to strike against non-state militias outside their jurisdiction on self-defence grounds remains to be established.

Pressure on politicians, recoiling in horror at the bloodshed, pushes towards a gloves-off approach based on reason of state. The state has reasons that reason itself cannot fathom. Against a background of xenophobia got up by Pegida, Le Pen, Wilders and the rest, we’re in a war whose very unwinnability prompts further self-defeating diktats. After meeting Hollande, Sarkozy, with an eye on returning to the Elysée in 2017, called for a tilt (‘une inflexion’) in French foreign policy towards Syria and Russia in order to smash Isis, even though Assad has caused around 95 per cent of civilian deaths in the civil war. Putin has run rings round occidental policy-makers in Syria, but a bilateral French tilt to Damascus is never going to fly, not least because French foreign policy needs to keep on the right side of the US and Turkey. Debate at this level is over different weapons to fight fog.