I'm not surprised to see a debate flaring up over the weekend about whether to call the brutal murder of British Army Drummer Lee Rigby an act of terrorism. See in particular the discussion between Andrew Sullivan and Glenn Greenwald, and this and this.

There are arguments on both sides. My initial response to the almost instantaneous labeling of the murder as 'terrorism' was to ask: if it is terrorism, what does that say about the countless Taliban and al Qaeda fighters that Western forces have killed in Afghanistan while those fighters were not directly engaged in warfare?

To be clear, I'm making a point about definitions, and am under no misapprehensions about the larger rights and wrongs. Rigby's service in Afghanistan was part of a war that, while politically misguided, was nonetheless just in its cause. Rigby, along with his colleagues in the UK Armed Forces, should be honoured for his service. By contrast, the men who killed Rigby are evidently allied to a cause that is in every respect unjust, brutal and totalitarian.

But Britain is fighting a war against al Qaeda and the Taliban in Afghanistan; acts of violence against serving soldiers far away from the battlefield are to be expected. If the British Army is hunting down a Taliban commander or bomb maker, it surely does not wait until he is on the battlefield with a weapon to hand to take action against him.

I heard one BBC journalist say on radio last week that it was poignant that Rigby should have survived his dangerous deployment to Afghanistan only to be killed in his own country. But of course, thousands of Afghan fighters have been killed in their home country in the last ten years. Their country is at war, after all. So is Britain.

There are countless definitions of terrorism, but one common thread is the use of violence against innocent civilians for political purposes. The 9/11 attack, on that characterisation, was clearly a terrorist attack. So was the Bali bombing and the recent Boston bombing. And yes, the London Blitz, the fire bombing of Dresden and the nuclear attacks on Hiroshima and Nagasaki were terrorist attacks too. The killing of a serving soldier cannot qualify as an act of terrorism on those grounds.

Yet those last few examples were acts perpetrated by states, and these days we tend to associate terrorism with what we loosely think of as 'illegitimate' combatants; that is, individuals or groups who do not identify openly as soldiers or fighters, even if they are working on behalf of a government. The murder of Drummer Rigby certainly did have that characteristic, and one other that we associate with terrorism: the event seems to have been staged not with some utilitarian military purpose in mind, but rather as a grotesque piece of theatre intended to (there's really no better word for it) terrorise the population.