How can we know that any piece of autobiographical writing is truthful? Where most reviewers and many readers of Diana Athill's Somewhere Towards the End have talked of its "honesty" or "candour", they have been making a literary critical judgment. Without checking any of its facts, they have come to believe the writer. The most important quality of the author may be her candour, but the most important quality of her writing is the confidence it gives the reader in that candour.
This last word is often shorthand for openness about sex. In fact, cannily and unconventionally, the book talks about the importance of sex rather than sex itself. Athill reviews her own sexual history for both the patterns it reveals and the satisfactions it recalls. She notices her belated preference for black men as a matter of plain fact, explicable partly because a lover who is "white and well-bred" was a "status symbol" for some black men: "Deplorable although I can't help being grateful for it."
This is not quite the form of autobiographical candour that we are used to valuing: confession. Ever since Rousseau, in his Confessions, turned a religious obligation into a secular compulsion, we have prized memoirs that tell us bad things. Confession means recording something shameful, something that is hard to tell. Athill contemplates the possibility of "digging out past guilts" and dismisses it as a fruitless occupation for "the very old" (as she ends the book she is 90). She is, instead, set on avoiding untruthfulness. This avoidance is something that the reader can test without knowing anything more about the author than what she tells us.
She tells us, for instance, about her affair with a married man whose wife has just given birth to their first child. She loves and admires him - all the more because he will not imagine abandoning "his good and blameless wife". "Leaving her would prove him cruel and irresponsible which I was sure he was not." The guiltlessness of this is slightly unnerving; the opportunity to appeal for sympathy is neglected. A characteristic sentence is one in which self-consolation is declined. Of her feeling that any man who proposed marriage was therefore undeserving of her: "I tried to believe it was something more rational, but it wasn't."
So "candour" seems a better word than "confession" for what makes the account of herself believable. A reader might be tempted to doubt her lack of regret about her childlessness if she did not so plainly admit to the delight of her few months of pregnancy before a miscarriage in her early 40s. "I suddenly became happy with a happiness so astonishingly complete that I still remember it with gratitude." It is there in her willingness to tell us how she acquired the three significant dents in her car, a beloved machine now that old age makes walking painful. The worst comes from getting herself trapped in a turning near Hyde Park and losing patience when she finds a bollard in her way. An "overtired old person flustered by her own silliness", she carries on regardless. Now she is"much ashamed" of her car's scars.
Some of her more surprising feelings convince us by surprising herself. Attending a mortuary to identify the corpse of her employer's mother, she notices her "odd excitement" at the working world of this place of death. "Had I been a dog my ears would have been pricked and my hackles up." Cleaning up the indescribable mess in a hospital toilet after a severely ill former lover has taken too effective a laxative, she is intrigued by her lack of disgust. This marks, she decides, "the automatic shift into wifehood", after a long period of "happy exemption". Charactersitically, she does not worry about the many readers who might themselves be wives.
A certain coldness is essential to this. She looks after her mother in her old age because she owes her "this consolation", but describes it as "suspending my life, which is what has to be done when living with an old person". "She is no longer able to adapt to other people's needs and tastes, and you are there to indulge her own." "She" is her mother, but also any such person, inflexible with age. Athill admits to a "nub of coldness at the centre", but also to being untormented by this recognition. She naturally treats it as a fact of her character, but it is also a matter of her style.
• John Mullan is professor of English at University College London. Join him and Diana Athill for a discussion on Wednesday 11 March at the Scott Room, The Guardian, Kings Place, York Way, London N1. Doors open at 6.30pm, talk begins at 7pm. Entry is £8 (includes a glass of wine). To book a ticket email book.club@theguardian.com or phone 020 3353 2881.
