Before you start

This is a short book and you can read it in two or three sittings. It's about one habit, and it belongs to two people. Something starts at ten. The dishwasher, the plan for Saturday, a tone. By eleven it's about everything, and by midnight neither of you can remember what it was about, and at one in the morning you're still on the sofa, because you were told never to go to bed on an argument, and you never have, and nothing has ever been settled at one in the morning that stayed settled at eight.

I'm going to argue three things. The first is that the habit makes sense from the inside. The old rule sounds like wisdom, leaving a row unfinished feels like abandoning it, and you can't imagine sleeping with it unsettled. The second is that the late hour is the worst hour of the day to settle anything, and there's research on why. Mood falls through the waking day. One night's lost sleep makes people more impulsive with anything negative. The same three points go round at one in the morning without moving, because the part of you that could move them has gone to bed already. And sleep doesn't let a row fester. It works on it, and the morning version is smaller and more accurate than the one you'd have settled at one. The third is practical. After ten, you don't settle arguments. Either of you can call a truce, you name a time tomorrow, and you go to bed cross if you have to. Chapters 20 to 23 cover how.

This book doesn't ask you to avoid conflict, to swallow things, or to pretend the row doesn't matter. The row matters. That's why it deserves the two of you at eight in the morning rather than the two of you at one.

Two cautions.

If the late arguments come with contempt, threats, or fear, or one of you isn't free to leave the room, that isn't a habit and this isn't the book. The National Domestic Abuse Helpline is free and open day and night on 0808 2000 247.

And if the rows are the surface of a low mood in either of you, low most of the day for a fortnight, that's a GP conversation, and the rows will be easier to have once it's had.

The notes at the back give my sources and their limits. Where I'm giving my own reasoning and not a finding, I'll say so.