In any modern war zone, whether it's Afghanistan, Gaza or Sri Lanka, armies confront  the problem: how far to go to minimise casualties to civilians when pursuing fighters in their midst.

There's a thoughtful essay on the subject from Avishai Margalit and Michael Walzer in the New York Review of Books, who take issue with arguments that the safety of soldiers takes precedence over civilians on the enemy side.

They write: "Conduct your war in the presence of noncombatants on the other side with the same care as if your citizens were noncombatants."