Why does the Islamic State engage in beheadings and crucifixions? Beheading is invoked in the Koran, but only the most extreme Islamic militants carry it out now.
We might identify three parts to this.
1. Psychological warfare is a key part of the Islamic State's military strategy
Even where outnumbered, as they were in Mosul in June, the Isil's fighters have used their reputation for terror to dissuade Iraqi forces from ever seeking battle. Which poorly paid soldier wishes to risk decapitation, impalement, or amputation for the sake of a distant, crumbling government? .
2. Brutality is a form of deterrence
Isil understands that Western governments are, to some extent, dissuaded by the prospect of a British or American soldier meeting a similar fate. It would mean not just political ruin, but also an unimaginable propaganda boost for the jihadist cause.
3. Propaganda by the deed
Terrorism is a form of propaganda by the deed. And the more chilling the deed, the more effective the propaganda. The graphic nature of beheading, the focus on the individual, and the act of bodily desecration involved all render this far more chilling than the explosion of a bomb, even where the latter's death toll is greater. The killing of Lee Rigby was uniquely horrific because of the mechanical quality of the murder.
There's little new in this approach, particularly the massacre of captives and the method of beheading for the purposes of terrorisation. The American journalist Daniel Pearl was beheaded in Pakistan in 2002, the American businessman Nick Berg in Iraq in 2004, and several others thereafter.
But does it all work?
There are two ways brutality can backfire. The first is that it can induce your enemies to fight even harder, because surrendering is such an awful option.
The second problem is that the Islamic State is in the state-building game. It is out to conquer, not merely to annihilate.
But it was precisely such excessive and indiscriminate violence that proved the downfall of the Islamic State's precursor, al-Qaeda in Iraq.
Although the Islamic State initially sought to restrain itself in the places it seized over the first half of this year, its record has been patchy. Iraqis may be accustomed to being ruled by terror, but it doesn't mean they like it. (© Daily Telegraph, London)