Book dedications can reveal more about a writer's personality, or their other half's, than the novels they preface, writes Susan Johnson.

When Samuel Johnson wrote that "the promises of authors are like the vows of lovers", we can assume he meant to describe something transient, of the moment. But does that make book dedications worthless? What happens to those heartfelt declarations of undying love when love is cold in the ground? If you are Graham Greene, you change the dedication. His 1936 Journey Without Maps was dedicated thus: "To my wife: 'I carry you like a passport everywhere'." Later editions came out with a terse: "To my cousin Barbara Strachwitz." Book dedications have been exercising my mind lately because my first husband has a new book out. We were married briefly, some 14 years ago.

Happily for him, his new book (Bangkok 8 by John Burdett) has been a hit this American summer, with enough buzz to suppose it might make that most literary of holy grails, the New York Times bestseller list.

The days have long gone since I would have ripped out the throat of anyone with news about him. That phase lasted perhaps a year or two, and then life moved on; we parted amicably enough, we had no children and no particular reason to keep in contact. Probably we would have lost contact altogether (we had no friends in common and did not even live in the same country).

I know it was I who thanked my brand-new husband in the acknowledgment pages of my second novel, Flying Lessons, with the unblushing words: "My love and appreciation, always." I know I once loved him, I know it hurt when we parted, but I can no longer feel the pain of it.

My life has moved on: a happy second marriage about to celebrate its 10th year, two sons, more books. Presumably, my ex-husband's life has moved on too; I wouldn't really know, were it not for book dedications.

It started in March. My literary agent rushed to tell me that the Transworld stand at the London Book Fair featured his new book. "It's dedicated to someone whose name I can't remember," she announced, "but it's not the same name that was in his last book." A friend in Australia e-mailed me in great excitement: "Ooh, I wonder who she is? How can you bear not to read it?" I probably won't read it, more because I'm not a fan of complicated thrillers, so I won't have a chance to scour the thanks and dedications.

But I like the fact that dedications offer a kind of archaeology of personal history. I like to think of T.S. Eliot, whom everyone thought of as buttoned up, snuggling up with his new young wife. He dedicated his 1958 play, The Elder Statesmen, to Valerie Fletcher, with the rather proud poem, To My Wife: "To whom I owe the leaping delight/ That quickens my senses in our wakingtime/ And the rhythm that governs the repose of our sleeping time, the breathing in unison."

I love, too, the fulsomeness of Thomas Wolfe (the original, not the contemporary Bonfire of the Vanities one), who dedicated his 1935 book, Of Time and the River, to Max Perkins, "a great editor and a brave and honest man, who stuck to the writer of the book through times of bitter hopelessness and doubt and would not let him give in to his own despair. A work to be known as Of Time and the River is dedicated with the hope that all of it may in some way be worthy of the loyal devotion and patient care which a dauntless and unshaken friend has given to each part of it, and without which none of it could have been written." Shortly after which Wolfe left both his publisher and his editor in a huff.

It seems to me that men are more likely to go overboard in the dedication department. It is perhaps no coincidence that men are the ones who thank their partners for everything, from keeping the children away to typing up the manuscript because, in my experience at least, it is male writers who have the most help.

Of course, there are exceptions: Hilary Mantel's husband, Gerald McEwen, is legendary for his support. Margaret Atwood's husband, Graeme Gibson, is also apparently such a saint that one American writer wanted to get a T-shirt printed with the slogan: "Every woman writer should be married to Graeme Gibson." However, Atwood's acknowledgments are always low-key. For Cat's Eye, a short: "Many thanks to Graeme Gibson for undergoing this novel." Other dedications are just a quiet: "For Graeme."

Male writers are certainly capable of the most pompous dedications, and Ford Madox Ford would be hard to beat. The famously ugly writer, who was astonishingly successful with a string of beautiful women (including a young and lovely Jean Rhys), wrote what must be one of the most self-regarding dedications of all time when The Good Soldier was reissued: "My dear Stella, I have always regarded this as my best book - at any rate as the best book of mine of a pre-war period, and between its writing and the appearance of my next novel nearly 10 years have elapsed, so that whatever I may have since written may be regarded as the work of a different man - as the work of your man. For it is certain that without the incentive to live that you offered me I should scarcely have survived the war-period and it is more certain still that without your spurring me again to write it I should never have written it again. And it happens that, by a queer chance, The Good Soldier is almost alone amongst my books in being dedicated to no one: Fate must have elected to let it wait the 10 years that it waited - for this dedication . . . And so I subscribe myself in all truth and in the hope that you will accept at once the particular dedication of this book and the general dedication of this edition. Your FMF."

And presumably, fate must have elected to have a pretty young thing walk in to knock poor Stella Bowen off her perch and out of FMF's affections.

Compare Madox Ford's dedication with the self-deprecatory humour of Helene Hanff (of 84 Charing Cross Road fame). Here she is dedicating her 1980 book, Underfoot in Show Business: "The day I finished the book, I celebrated by phoning Maxine in Hollywood. 'Do you want to hear the dedication?' I asked her. 'Go ahead,' said Maxine. So I read it to her: To all the stagestruck kids who ever have, or ever will, set out to crash the theatre. 'What do you think of it?' I asked. 'It's much too sentimental,' said Maxine. 'Why don't you just dedicate it to me?' So what the hell - This book is for Maxine." Speaking personally, I would never change a dedication. The only time I did was when I inadvertently upset a friend by mentioning her in passing in a memoir. I removed every reference to her in subsequent editions.

I like the idea of my dedications, and my ex-husband's dedications and all dedications in general, leaving a kind of trail of our lives. And in the future, his books and their dedications will continue to bring unasked-for news of him, just as mine will to him.

Susan Johnson's last book, A Better Woman, is published by Aurum Press