Here's a question for you: why, exactly, are British forces fighting - and dying - in Afghanistan?
No army likes to go into battle without knowing why - and the government seems to be having some difficulty in coming up with an answer that works.
This was Harriet Harman, standing in for Gordon Brown at Prime Minister's Questions on Wednesday: "It is important to make sure in the mountainous regions surrounding Afghanistan and Pakistan (that) we do not have a crucible for the development of terrorism that threatens not only the people in that country but the region and indeed the whole world."
Sub-text: remember 9/11?
The new defence secretary, Bob Ainsworth, said pretty much the same thing in more detail the same day. The priorities are, he said, (i) "to prevent a return to Taliban control that allowed terrorists to flourish and threaten our national security; (ii) to prepare the way for elections ... by confronting the insurgents, denying them the freedom to operate, isolating them, and degrading their capability; and (iii) to provide the time and space for the Afghan forces to take responsibility for the security of their people, and for the Afghan Government to build their civil society."
The key message from the government, then, is simply this: if you want a secure Britain, you have to help create a secure Afghanistan. In the words of Bob Ainsworth: "Our troops are in Afghanistan to keep our country safe from the threat of terrorism."
Simple. Except, of course, it isn't.
Critics like Simon Jenkins, writing in The Guardian, say our military involvement in Afghanistan is unhappily reminiscent of how the US became embroiled in Vietnam. "Vietnam began with Kennedy's noble 1963 intervention, to keep the Communist menace at bay and thus make the world safe for democracy. That is what George Bush and Tony Blair said of terrorism and Afghanistan."
No one is arguing that military force alone will create a safe and stable Afghanistan. (After all, the British army tried and failed more than once in the 19th century - and the Soviet army failed just as dismally in the 1980s.) The argument is whether the political progress that needs to be made can be achieved only with military assistance, or rather whether it will come, if at all, only when the foreign forces have departed.
As for the "winning hearts and minds" argument (yes, it was heard in Vietnam too), Jenkins is scathing: "The strategy of 'hearts and minds plus' cannot be realistic, turning Afghanistan into a vast and indefinite barracks with hundreds of thousands of Western soldiers sitting atop a colonial Babel of administrators and professionals. It will never be secure. It offers Afghanistan a promise only of relentless war, one that Afghans outside Kabul know that warlords, drug cartels and Taliban sympathisers are winning."
But might Iraq be a useful example? Most commentators seem doubtful. For one thing, Iraq and Afghanistan are very different places, topographically, ethnically, culturally and historically. Yet critics say that much of the military thinking in Afghanistan does seem to be based on what has already been tried in Iraq. (Not really surprising; after all, the US General David Petraeus is the strategic mastermind in both countries.)
Those who doubt the wisdom of British military involvement in Afghanistan say the government is sending our soldiers to fight a war they cannot win.
Those who support the current strategy say that to pull out now would hand the country back to the Taliban - which most Afghans don't want, and which would put the UK at risk of terrorist attack - and send a dangerous message of weakness to any other potential insurgent groups who may be tempted to follow the Taliban example.
What do you think?