How to stop buying books you already own

Buying a second copy of a book you already own is one of the most common complaints of anyone with more books than they can hold in their head. It rarely means carelessness. Past a few hundred books, memory stops being a catalogue, and the circumstances of buying — a crowded sale table, a shop with no time to think — are the worst possible moment to rely on it.

• The cover changed. Publishers reissue the same text with new jackets, and a book you would know on your shelf is unrecognisable in a shop.
• The title changed. Some books are published under different titles in different countries — Harry Potter and the Philosopher’s Stone is Harry Potter and the Sorcerer’s Stone in the United States — and some are retitled for a later edition.
• Somebody else bought it. In a household, a book one person bought last year is news to the other.
• It is one volume of a series. Remembering that you own "some of" a long series is not the same as knowing which numbers.

The fix is a list of what you own that you can consult from where you buy books — which in practice means from your phone. It has to cover the whole household’s books, not one person’s, and it has to be the same list for everyone, or the household case above still happens. A spreadsheet works if someone keeps it up; the test is whether it is current and whether you can search it standing in a shop.

• Scan or type the ISBN. It is the fastest check and the most precise: it tells you whether you own this exact edition.
• Then check the title. An ISBN identifies one edition in one format, so the paperback of a hardcover you own has a different number and a barcode check will call it new. Searching your list by title and author catches other editions and formats.
• Check the author, too, when the title draws a blank. That is how a retitled book or a foreign edition turns up.
• For an older book with no barcode, check by title and author — and, if it has one, by the Library of Congress number on the copyright page.

Whether a second edition counts as a duplicate is your call. Collectors often want the first edition and the illustrated edition and the one with the different introduction; the check is there so that the second copy is a decision, not a surprise.

The other half of not buying the wrong book is remembering which ones you meant to buy. A want list — the editions you are looking for, the volumes missing from a series, the book a friend recommended — turns "do I already have this?" into "is this one of the ones I am after?". Note the edition you want, and a price you are willing to pay, while you are calm at home rather than at the sale table.

For a book sale or a shop with no mobile signal, print the want list and take it with you. It is the oldest method there is, and it still works.

Once everything is catalogued, the duplicates show themselves. Not every one is a mistake: a reading copy and a good copy, a copy for the cottage, two editions you value for different reasons. Record those as deliberate. The rest are the easiest books in your collection to pass on — to a friend, a library sale, a church book table or a charity shop — and the cheapest way to make shelf space.

• How to tell if a book is a first printing →
• What an ISBN tells you about a book →