THROUGHOUT AUGUST IN Edinburgh we are privileged to hear a host of superlative authors. Salman Rushdie and AL Kennedy, Yang Lian and Sylvie Germain: it seems as if, for a few weeks, a corner in the West End of Edinburgh partakes of a small measure of immortality. Charlotte Square becomes, in the words of poet Robert Lowell, "the minor slopes of Parnassus". I am there, in a way, in a role akin to that of the slave whom Julius Caesar had next to him on his triumphal processions, whose job was constantly to whisper, "You too are mortal."

To explain, let me take you, Doctor Who-style, to four places: Athens in 416 BC, London in 1613, Cardiff in 1953 and Edinburgh 11 months ago.

In 416 BC, the philosopher Socrates was drinking at a celebration symposium with two playwrights: Aristophanes the comedian and Agathon the tragedian. Agathon had won first prize in the annual dramatic competition, fending off both Sophocles and Euripides. He was famous enough to be quoted by Aristotle, and lampooned by his comedic co-boozer at that party. He had also done the unthinkable: created plays with plots of his own devising. Rather than recasting myths and legends, he wrote an original play, The Flowers. Only a smattering of his lines survive.

In 1613 the court in London was entertained by a new play, Cardenio. Whatever the esteemed guests thought of it (and there were ambassadors in the room) it was included in a list by the Stationer's Register in 1653, for imminent publication, and adapted for modern sensibilities in 1727 by Lewis Theobald, under the title Double Falsehood, or The Distrest Lovers. The manuscript was destroyed, presumably in a fire in Covent Garden in 1808. What makes all this unbelievable is that Cardenio was by Shakespeare.

In 1953 Dylan Thomas had enjoyed reading from his new "kind-of-a-play of mine" to an audience in Cardiff. Whatever happened, and given Thomas's lifestyle one may presume that a drink had been taken, he wrote to his host afterwards asking if a briefcase had been left anywhere. The tone of the letter is half-resigned, half-hysterical: after all, it did have the first draft of Under Milk Wood in it. Thomas managed to lose the manuscript a few more times, but also forgot to complete many other inspirational projects: a translation of Peer Gynt for example.

In September 2004, someone opened the window of the house where my wife and I live and nicked my laptop. That evening I had put the finishing touches on the book I had been writing: The Book of Lost Books, a history of the literature that was destroyed, unstarted and unfinished, a compendium of books that could never be read, my personal library through the looking-glass. Luckily, I had e-mailed the text to my publishers before retiring, woozily and triumphantly, to bed. Thus, The Book of Lost Books narrowly escaped being part of its own subject matter.

A word often used to describe great literature is "deathless", and, frankly, authors have been instrumental in this assumption. "I have created a pyramid more lasting than bronze," wrote Quintus Horatius Flaccus. "The poet's words are always hovering around the Gates of Paradise, knocking softly, beseeching and gaining eternal life," opined Goethe. Immortality is not, however, the norm: loss is the inescapable rule of the literary universe.

From Homer to Hemingway, the great and the good are only apparent to us in a fractured form. They are badly taken photos, with an arm or a hat missing. Homer, as well as writing The Iliad and The Odyssey, wrote a comedy epic called Margites. Hadley Hemingway misplaced her then husband's entire creative endeavours to date. And is loss so bad anyway? Would Hemingway have taken the advice of Ezra Pound and ditched the lot, if it hadn't been snatched anyway? Umberto Eco made the loss of Aristotle's second volume of Poetics, On Comedy, the linchpin in The Name of the Rose. But imagine if we did have as strict a template for comedy as we once had for tragedy: no As You Like It, no Bartholomew Fair, no Tartuffe, no Pygmalion: maybe one extinction is worth such flourishings.

There are other authors I could not even begin to uncover. Who was the first female Muslim poet? The first Jewish chronicler? The first human to make a poem, and write it down? And was it a hymn, a riddle, a song of triumph, an elegy for a partner or a satire on a neighbour? Though we love to imagine literature has a permanent quality, all of history suggests otherwise.

Writing The Book of Lost Books was unmitigated pleasure and utterly essential. Since childhood I had been an avid, if erratic, collector as well as reader. My grandfather recalls me phoning him when I was five, listing the Mr Men books not to buy me since I already had them. My father, stuck away from the family on a teaching guidance course in Glasgow, had to endure my tantrum when I realised the Doctor Who book he was describing was one I already had.

The roots of the book's necessity are there: I'm a nerd. A sci-fi nerd, a completion fetishist, a literature guzzler. The pleasure part was going into libraries and deciding what might intrigue me that day. My own book dragged me into Arabic poetry, the transition between shogun and chonin subjects in Japanese, late Roman mathematics and the worse excesses of the Holocaust. It nudged me the whole time, making me skip the spines and alight on the enlightening.

But it is needful to remind ourselves that what we take for granted may not be so persistent. Do grants from state bodies guarantee permanence? Look at Agathon. Does a "big name" mean your work is perpetually famous? Look at Shakespeare. Does being shocking preserve your notoriety? Look at Burroughs, whose typed pages were on sale in North Africa after he decided a flit was necessary, and who never turned back to look at those pages that never made it into The Naked Lunch.

Literature, as we have it, is a shoogly proposition. More is gone than has been retained, more was lost than is treasured. For every vigorous new voice there is a maelstrom of anonymity, for each bunch of indecently talented writers awaits a vortex of void. Ask Xenocles, Cynewulf, Torquato Tasso and Frank Norris: in their days, praised; now nigh unknown. Every author in my book is a mere representative of centuries of failure.

For me, The Book of Lost Books was a bit like being Scott's Old Mortality, tending the graves and rejoicing in the memories of those who are infinitely better, but gone beforehand. I hope the book reminds people of the days when booksellers had whole walls devoted to "the classics". It was there and then, back in the not-so-long-ago 1980s, that I found names I had never seen, heard or read before: Hesiod, Camoens, Melville, Gogol and Pound. Everyone deserves the chance to stumble on the greats; and make them their own. Writing The Book of Lost Books reminded me what literature is about: not the next biggest thing, but the oldest, strongest, most bizarre and most accessible thing.

Stuart Kelly's The Book of Lost Books was published this week by Viking, £15.99. He will be at the Edinburgh International Book Festival on Monday 29 August.