We all know where to find an index. It’s at the back. The physical form of the book – a bundle of flickable leaves clapped between two covers – has had such an astonishingly long run that it’s hard to imagine its major features arranged any other way. That hasn’t always been the case. The title page, for example, which we confidently expect to find at the front of every printed book, didn’t catch on for decades. Page numbers were another feature that Gutenberg and his first imitators felt they could do without. And with no page numbers as locators, how would an index work?

As Dennis Duncan shows in his puckish eulogy to this often overlooked appendage, the index has a long history, longer even than printing itself. It turns out that the first attempts appeared at the front of the book. Come to think of it, what’s wrong with an index at the front?

The index was always a reading aid waiting to be invented. Without any indication of what it contains, a book remains, well, a closed book. Duncan delves back as far as the fabled library of Alexandria, where Callimachus would perhaps not have compiled his famous catalogue of all the library’s scrolls had they not first been tagged with contents labels, parchment tags that the Greeks called sillybos, whence our word ‘syllabus’.

Duncan connects the invention of the index proper to the 12th-century explosion in preaching, inspired by the new mendicant orders. To the medieval Christian, there was one book above all others: the Bible. A speciality index, a concordance, listed each occurrence of every single word in it. That was all well and good, but a friar wishing to preach a sermon on a passage that included, say, a camel, would need to know more about it than merely how many times it was mentioned in the Bible. What was God trying to say by alluding to camels? What even was a camel? For that, the preacher could consult one of the great medieval encyclopedias, such as that produced by Isidore of Seville. The earliest attempts at indexes, with compilers taking their cue from encyclopedias, were arranged by subject. Learned scholars, Duncan suggests, considered alphabetical order to be gauche.

Duncan has his heroes, one of whom, the capaciously skulled Robert Grosseteste, really seems to have been named for the size of his head. Grosseteste was of the generation who heard the Franciscan call and renounced worldly wealth for a life of study, preaching and writing. Extremely widely read, Grosseteste created his own indexes with complex glyphs to use as locators, allowing him to retrieve all his hard-won knowledge. The problem he faced was that, even with page numbers added by hand, his indexes, no matter how ingenious, referred solely to one specific manuscript. It was only once printing had standardised the number of pages in any given edition that a single index could serve every copy.

If indexes are so useful, why don’t novels have them? With his eagerness to scurry down each and every rabbit hole, a tendency that makes this book a trove of bookish anecdote, Duncan unearths examples of novelists using them as fictive playthings. J G Ballard produced an entire story in the form of an alphabetical index, inviting the reader to reconstruct the missing book from its surviving index, while in Nabokov’s Pale Fire, Charles Kinbote, the deranged editor of the titular poem, runs amok, producing an index that attacks the poem and its author.

Kinbote is not the only person to have wielded the index as an offensive weapon. The 18th-century historian John Oldmixon had an underdog’s appetite for controversy. When offered the drudge job of indexing Laurence Echard’s History of England, a work with a strong High Tory bent, Oldmixon seized the opportunity to make mischief. As Duncan shows, his index undercuts Echard’s intended meanings with sarcastic and deliberate misrepresentations, rewriting history from the safety of the back pages. Oldmixon’s is the ultimate index compiled in bad faith.

Mark Twain’s Adventures of Huckleberry Finn has something approaching an index, opening with a list of the book’s chapters, each with brief tags describing the episodes within. Twain’s chapter summaries don’t quite meet Duncan’s definition of an index, however, as they neither include references to pages nor are ordered alphabetically. For Duncan, these are essential features of an index.

The novel sans index taunts us with the knowledge that if we want to go back and find something, we will need to have noted down the exact page number; otherwise we will need to wade through the whole thing again. Duncan suggests that this represents a recrudescence of an earlier anxiety that an index would serve as a lazy substitute for reading the entire book. With an index, will readers pick out only the good bits?

The index may have found its niche at the back of the printed book, but is it obsolete in the digital age, in danger of being killed off by the word search? Or is its 21st-century reincarnation merely hiding in plain sight? As Duncan points out, Google is really just an index, albeit a gargantuan one.

And what of this wittily engaging, wide-ranging book’s own index? Duncan playfully offers two, the first generated by computer. Surprisingly entertaining, it chops the book into small chunks and regurgitates it almost at book length. Duncan pulls the plug at the entry for ‘amusement, mere’ and hands it over to a human indexer, Paula Clarke Bain, who shows how the job ought to be done, with some amusing running gags thrown in for good measure.