"The great example of an informal truce is the Christmas truce of December 1914.
"Quite conspicuously, the troops simply get out of their trenches, bury the bodies of their mates who have fallen in no-man's-land, and then converse with the enemy (in so far as they can converse), sing Christmas carols in their respective languages, swap cigarettes, show each other photographs of their families and maybe take a look at one another's trenches to be able to learn something for another day.
"This is a bit like a family that is driven by a terrible quarrel, so that they hate each other's guts and are not on speaking terms. But on Christmas Day, they get together and talk about peace on earth and goodwill towards men – on the assumption that after Christmas, they'll go back to hating each other, warring with each other.
"The Christmas truce doesn't mean that there was some act of rebellion against their own commanders going on. It just means that Christmas Day is supposed to be a day of exceptional pleasure and enjoyment. And in terms of being in a trench, this was exceptionally pleasurable and enjoyable.
"Now a sort of muted example of this takes the form of live and let live. As long as you weren't actually going to attack the enemy, as long as you weren't trying to kill them to some purpose, or run the risk of being killed to some purpose, you might as well make life as comfortable as possible for each other.
"… and so certain informal ways of behaving developed.
"You fired your bombardments at particular times of day. The command had made it clear that a certain number of shells had to go over every day in order to make life miserable for the enemy. But, okay, you sent them over, but not at that time of day when the enemy would be having dinner, because on both sides meals were a terribly important part of life in the trenches on the Western Front.
"They were the things you looked forward to, that you cared about. If your dinner didn't reach you, if supplies didn't come along the communication trenches, then you were really having a miserable time.
"Well, one way that you were going to prevent yourself from having a good dinner was to bombard the enemy at dinnertime because he would retaliate. If you made life exceptionally miserable for him, he'd make it exceptionally miserable for you.
"So an unwritten arrangement developed that if you had to fire a bombardment, you wouldn't do it at these absolutely key times.
"And often you wouldn't fire at a position that was likely to hurt many of the enemy. You didn't fire at their trenches, but beyond their trenches. That way you've done your duty, you've fired off the required number of shells, you've shown you were hostile and in fighting mode, but you haven't actually done the enemy a lot of damage. At the same time, he hasn't done you a lot of damage either, and so you can live to fight another day.
"You are alive to fight on a day when you're fighting to some purpose."