What do we mean by ‘rare’? That may sound a little like Lewis Carroll’s Humpty Dumpty: ‘When I use a word … it means just what I choose it to mean – neither more nor less.’ The online Cambridge Dictionary offers a more mundane answer: ‘1. not common; very unusual: 2. (of meat) not cooked for very long and still red: 3. used to describe the air at the top of a mountain’. But if we try to apply one of these definitions to what are commonly referred to as rare books, we quickly find that language does not always match dictionary definitions. The first definition provided by the Cambridge Dictionary will not suit our purposes, for the books that are most commonly referred to as rare are sometimes very common. Several hundred copies survive of the First Folio of Shakespeare (1623). Around nine hundred copies survive of the Nuremberg Chronicle, a giant-sized illustrated history of the world from the Creation to modern times, printed at Nuremberg in 1493. These are larger numbers than have been printed of many, perhaps most, academic books published in the last thirty or forty years, as demand has declined and publishers have become unwilling to pay for storage costs spreading perhaps over many years of slow sales. Yet we would not usually describe modern academic books as rare in the way that we think of the first collected edition of Shakespeare.

If you look on the internet, you will soon see more of this confusion. In particular, there are books that are sometimes unofficially referred to in the trade as ‘trophy’ books: that is, books regularly described as rare that carry high prices unrelated to their scarceness or the difficulty of finding a copy. The first edition of Darwin’s On the Origin of Species (1859) is an obvious example. So is the first edition of Newton’s Principia (1687). Both demand many pounds or dollars, but both come up regularly for sale, at least in straightforward copies (special copies, such as those having a well-known provenance or in exceptional condition, naturally demand a premium). Some modern books fall into the same category, such as the three volumes of the first edition of The Lord of the Rings, or the first Harry Potter book, or the first James Bond novel, Casino Royale. Copies must of course still have their original dust jackets and be in fine condition.

Thus rarity (in the sense of scarceness) and price do not necessarily march together. If we are to understand the term, we must look further. In order to appreciate its wider meaning, it is perhaps useful to go to another word: ‘curious’. This was a term much used in the 17th and 18th centuries to denote things that were not only uncommon but also of uncommon interest. In 1718 the Oxford bookseller Stephen Fletcher issued ‘A Catalogue of Curious, Rare, and Uncommon, Books, Both Ancient and Modern’ to be sold at auction. In 1781 the Edinburgh bookseller Thomas Philipe chose very similar words for his ‘Catalogue of Curious, Rare, and Useful books’. In the 1740s the London bookseller Thomas Osborne selected from the enormous library of printed books assembled by Lord Harley, to issue several volumes of ‘Scarce, Curious and Entertaining Pamphlets and Tracts’. All the pamphlets that he reprinted would now be accounted rare or scarce, but at the time he needed also to indicate that they had a further value, whether to satisfy curiosity or to entertain.

Something of these further considerations is reflected in the way that we now talk of rare books. The category includes not only books and pamphlets that are scarce but also those that are in some way unusual or require special attention or care. Financially, if they are modern or recent, they may be worth very little. Many books that we now see as common will in due course be categorised as rare and start to be appreciated for all kinds of unpredictable reasons. To take very simple examples: cookery books and children’s books published two hundred years ago are now rare by several definitions, and valued accordingly. Originally printed in large numbers, most copies have been used to destruction, and surviving versions have become scarce. They have a further historical interest too. In their worn states they can speak to us of past lives.

All these books, whether in good condition or bad, are also to be valued as physical objects in and of themselves, not just as objects of financial value. Many books have been scanned by libraries and commercial firms in their entirety because they are, or seem, rare in some sense. The resulting opportunities for online reading have transformed our understanding of the past. But each physical copy is different. Its physical condition, the notes and scribbles it contains, its marks of past ownership, its binding and its paper tell us far more than what we may discover on our screens. In other words, rare books can be as interesting for their ordinariness as their scarcity. If we look in institutional or private libraries today, much can seem ordinary. But the ordinary can itself be of rare value.