One of the basic laws of traffic is said to be that supply creates demand: widen a single to a dual carriageway, and it will soon be clogged. Build a motorway and watch the traffic thicken till it congeals. Something analogous happens to owners of books. Buy yet another bookcase, or erect a shelf along one of the few walls still free to take one, and sooner rather than later you will be doublestacking again, then balancing your extra books on the tops of the others. Some people have a sufficiently sensible, or ruthless, streak to avoid this, by having periodic purges: others, equally determined to throw out enough of their books to make some real space, begin boldly by placing a large cardboard box in the middle of the room, only to find that after an hour it contains only one or two rotting paperbacks. Others, mysteriously, even though well-read and clearly also buyers of books, never seem to have any such problem: their shelves, always filled but never crammed, gleam at you in mocking trim. For many, the problem remains a vicious circle.

Whether you are a hoarder or a weeder, if you buy books it is likely that you will regularly make the situation worse: though there are some which you are happy to borrow from the library, there will always be others which you are unable to resist acquiring. Recently this has meant, for me, Seamus Heaney's Electric Light (which includes a poem ...