We read from left to right and from start to finish. Or do we? We dot about, skimming and scanning. We check out the bibliography or the index before we get our teeth into the text itself. We wince at fulsome acknowledgements, wonder at voluminous notes, and vow to read other books by the same author before we’ve finished the one we’re on. We don’t, in fact, read from start to finish. The Norwegian novelist Dag Solstad’s Armand V (2006) sends up this tendency: the story is told exclusively in footnotes.

Bibliographers and librarians are specialists at reading texts in reverse, gathering the essence of a book from what materials they can lay their hands on in as little time as possible. Take, for instance, the crime novel Soul Circus (2003) by the American author George Pelecanos. The Library of Congress classification annotations may seem oblique, but they distil the essence of the book in a few words: ‘1. Private investigations – Washington (DC) – Fiction. 2. Washington (DC) – Fiction. 3. Drug traffic – Fiction. 4. Title’.

You don’t need to be a bibliographer to read in reverse: we all do it, all the time. One quick-fire way to evaluate a book is to go straight to the bibliography to see what the author has read. But to get really intimate with the text, turn to the index (contents pages are not enough and are often cryptic anyway). Indexing involves dissecting, cross-checking, systematising, reconceptualising and illuminating – in other words, anatomising a book.

What are we looking for when we turn to the index? First off, we search for interesting symptoms in the narrative patient. Take John Eliot Gardiner’s Music in the Castle of Heaven: A Portrait of Johann Sebastian Bach (2013). Its index immerses you not only in Bach’s music and creative process (‘singleness of purpose’, ‘perfection quest and habit’), but also in the events of his life – eye operations, for instance, or the deaths of his parents. There are unexpected revelations too, such as mathematical images in the St John Passion, to take one example. We diagnose as we read.

An even better example is the index to Laurence Bergreen’s biography of Irving Berlin, As Thousands Cheer (1990). By reading in reverse, the essentials of Berlin’s life can be quickly discovered. Under ‘Berlin’ you’ll find an alphabetical list of episodes in his life and telling traits: ‘abusive phone calls by’, ‘business sense of’, ‘childhood memories of’, ‘denial of harsh realities by’, ‘nervous energy of’, ‘as singing waiter’, ‘youthful poverty and hardship of’ and so on. There you have it: a complete guide to his life in a few pages for the reader with little time but an awakening interest. Reading the rest of the book puts flesh on the bones.

But that is not all that reading in reverse can do for you. Like the old Dent Everyman’s Library, it can be a guide for and friend to the uninitiated reader. Take, for instance, Jane Austen’s letters. The collection put together by Deirdre Le Faye, published by Oxford University Press, is the go-to version (I have the fourth edition, which appeared in 2011). It’s a masterwork of seven hundred pages, half of them devoted to notes and indexes. These include a biographical index (you can separate out the Cravens, the Fowles and the Lefroys), a topographical index (there are entries for Bath and Southampton, White’s Club and Astley’s Amphitheatre), a subject index (which includes such categories as fabrics, jewellery, domesticity, indoor games and social etiquette, and individual entries on ‘darning stockings’, ‘wash-days’, ‘chintz’, ‘bad breath’, ‘distribution of wedding cake’ and even ‘viewing a corpse’) and, just in case, a general index. The whole world of Jane Austen is reproduced in miniature for effortless navigation.

Then there is The Portable Atheist (2007), ‘essential readings for the non-believer’ selected by Christopher Hitchens. Atheism is a conceptual minefield, so you need an intelligent index to help you through, adding something to the forty-seven passages selected, which include offerings from the likes of David Hume, Bertrand Russell and A C Grayling. Adversarially, Christianity needs dealing with, along with apostates, Hobbes, the Second Coming and Spinoza. So too does evolution (‘see also Natural selection’), Charles Darwin, Alfred Russel Wallace and Richard Dawkins. Then there are the big ones: God (‘alleged evidence of existence’), Jesus (‘atheists for’), heaven, hell, Catholicism and the Resurrection. Tantalising terms abound – prayer, miracles, soul, sorcery – and there are suggestive names too (‘Houdini, Harry’). Reading in reverse unpacks the concepts you need to find your way around the passages and, in the process, become a good non-believer.

Reading in reverse, then, doesn’t mean just sneaking into the last chapter to find out whodunnit or treating books like useful tools and study guides. We do it intuitively. Nowadays, if there is no index, we go to Google Books to look for references. But the index is not just a superseded version of the embedded digital link. It’s an active player in the process of reading, guiding us through complex narratives. Where an index is lacking, readers will create their own. I have seen copies of Emma, Vile Bodies and Animal Farm indexed by conscientious owners in scribbles on the flyleaves. Hymn books too. The motive may be pragmatic, making it easier to find particular passages in the text in future, but it is also about reflective and analytical reading. Reviewers often lament the absence of indexes in books. All of us should share their regret.