We talk about peak oil without agreeing whether or not we have reached the plateau yet. The case of letters is, arguably, bleaker by far. People don’t write letters any more. Effectively, we have been running out for years. What can we look forward to? Maybe the odd cache of ancient love letters, combined with the droppings of the few remaining twentieth-century refuseniks who never took to the blower, and then it’s over. Of course it doesn’t feel as though we’re running out (does it ever?). Last year we read, or read about, new editions of letters by the Mitford sisters, Graham Greene, Noël Coward, Arthur Conan Doyle and Ted Hughes. The Victorian Life and Letters formula murdered by Froude and buried by Strachey has never been revived, but A Life in Letters is a popular postmodern stand-in, especially when one or more biographies are already in circulation. Indeed, a common sequence is for literary estates to appoint official biographers to get something out in the years immediately after their subject’s death. The letters, meanwhile, continue to be collected and worked on by someone else, and are eventually published in a scholarly edition a good while later. The existence of a full edition of the letters then generates another biography or two. And so the show goes on.

Except that it won’t. Not for much longer, because no one writes letters any more. Pity the biographers of the future; pity their readers.

This was the thought with which I embarked, several months ago, on some intensive butterfly reading, flitting from letters to lives and back again as I stalked ‘a book about letters’ which I had agreed to write without knowing how. But increasingly I wonder whether biography and letters are indeed natural bedfellows. The best biographers dare to imagine themselves as their subjects; the best letter-writers don’t need an intermediary. The biographer seeks to raise a ghost but the letter is a ghost that can be disappointingly laid to rest by the biographer holding it up to the light, engaging and criticising and generally getting in the way of what is otherwise a first-hand encounter, albeit of an eavesdropping nature. The instance I keep returning to is the case of Jane Carlyle, married to the once eminent, now virtually unread Victorian colossus Thomas Carlyle. She also wrote, but she wrote only letters: dashed-off affairs about nothing much – her house, her servants, her husband, her insomnia, his dyspepsia – which succeed, time and again, in catching life on the wing. What a pity she did not write novels, said her contemporaries. I think Jane Carlyle did not write a novel because she could not. She was not a maker-upper. The only history she could write was the history of her own life and she did this superlatively well. The Carlyles were childless and (almost certainly) sexless, and her portrait of their often uncompanionable companionship has the intensity of nightmare. Theirs was a marriage with none of the distractions which the married arrange for themselves to dilute the mix: pure marriage, you might say, and, as such, almost undrinkable. Her letters are so vivid and so self-mocking in their various martyrdoms that it is impossible to read Jane Carlyle and not love her. But let a bossy-boots biographer into the compact and the love affair is compromised. There are individuals whom it is better to learn about than know, but Jane Carlyle belongs in the opposite camp. Of course, if a third party were to sketch the portrait of a sexually frustrated, neurasthenic junky (she had a morphine habit, for a time) who made mountains out of domestic molehills, you might well shrug and say she should have got a life. But Jane Carlyle’s life was putting the ungot life into words. It may be a question of ‘listen and enjoy’.

Jane Carlyle was an artist. Or was she? ‘Letters are not literature’, wrote Virginia Woolf, who knew a thing or two about both. Later she would relax sufficiently on the question to refer to letter-writing as ‘the humane art which owes its origin to the love of friends’, and went on to fear for its future:

News and gossip, the sticks and straws out of which the old letter-writer made his nest, have been snatched away. The wireless and the telephone have intervened. The letter-writer has nothing now to build with except what is most private; and how monotonous after a page or two the intensity of the very private becomes! … Instead of letters posterity will have confessions, diaries, notebooks, like M Gide’s-hybrid books in which the writer talks in the dark to himself about himself for a generation yet to be born.

How right she was, and yet how wrong. Thanks to email, news and gossip are once more disseminated by means of personal correspondence. The return of the written word as a tool of communication is one of the great advances of recent years. Not least because it is once more possible for latter-day Dorothy Osbornes – fierce shy ones who can’t speak without blushing and for that reason don’t – to show off their mettle in muscular prose. Yet it is not at all clear that emails will be collected and bound and edited and offered to the public in the same way that letters have been. Who keeps their emails for starters? Geeks and fools and horses may trust to the Tower of Babel of modern technology – the rest of us know that paper money is the stuff which counts. And do we print out our emails? Most of us are too lazy or tidy to bother. Others, greener and meaner, won’t on principle. Injunctions to ‘consider the environment before printing out this email’ even occur now at the foot of communications from the Times Literary Supplement. But where would the TLS be without the paper trail?