You are the outstanding literary critic and essayist of your generation in the English-speaking world as well as being a fine novelist and playwright. You live with your mother for fifty-six years, the age you are when she dies in 1996 at eighty-five. You alone are in a position to record her early life, and then your life together. Such a classically potent theme undoubtedly lends itself to fiction, and connoisseurs of this writer will see some of his novels - e.g. Contre-Jour - through a different prism after reading A Life, which is a biography of his 'passionate and ascetic' mother, the poet and translator, Sacha Rabinovitch. The author tells us that one of his novels may have upset her because he drew quite ruthlessly on a painful episode from her personal life, but she never discussed the account with him. And the end of the present book would certainly have shocked the shy and reticent Sacha with its medical revelations of her final months. But one suspects she would not have been surprised, for almost by definition a biography of one's mother and cohabitee is to some extent an autobiography. This non-fictional book-length portrait of a mother has only one rival, Edward Dahlberg's rhapsodic account of his early life, Because I was Flesh.

One of the many virtues of Josipovici's extraordinary book about a brave and remarkable woman is that it openly confronts difficult questions that modern readers of such a story will ask. Thus, did the orphan mother and deserted wife compensate by becoming over-dominating and tyrannical? And, even if she did, was the son too weak-willed to make his own way in the world after, say, graduating from university or meeting a future wife? Was the son's permanent presence until she died the reason why she never remarried and, indeed, he himself never married? Or were the special circumstances of their early years together the matrix of a unique situation, a motherson relationship which somehow transmuted into a robust friendship between equals, two writers who loved each other as friends while just happening to be mother and son? There is a poignancy about one particular comment in what may be Josipovici's best book, Touch: '...the miracle that takes place in every human life when we are forced to let go and find that we can actually make it on our own, when we reconcile ourselves to letting go and find that those we have nurtured can actually make it on their own'.

We learn that Josipovici had girlfriends but, unlike the Jewish mother from Kansas City a century ago, Lizzie Dahlberg, Sacha does not appear to have sought or even wanted a husband. Josipovici's book asks us to believe in this unusual friendship, and such are the author's powers of persuasion - thanks to a prose style forged out of a marriage between literary criticism and fiction which generates a subtle and authoritative vehicle for a close examination of two lives - that we are inclined to believe him, despite sporadic and legitimate reticence about himself. In any case, even a reader more sceptical or cynical about the relationship than myself will be fascinated by the factual story which begins - for the author at least - with his birth in Nice on the very day his mother could otherwise have left Vichy France, her passage booked on the last boat to Egypt out of Marseilles: 8 October 1940.

It is clear that Josipovici has a high ambition, namely to track and trace the trajectory of a lived life - terminal illness too is part of life - and because the author is a real writer he is not exclusively interested in the intermittent high dramas which punctuated the life. At the heart of the book, formally and emotionally, are a professional literary critic's loving meditation on and unsentimental interrogation of two sets of documents: mundane family photographs and the mother's poems. The (sadly unscreened) photographs are brilliantly 'developed' in the manner of Roland Barthes rather than W.G. Sebald, and Josipovici's analysis of their series circuit will surely inspire some readers to meditate on the significance of previously unheeded gestural details in their own family albums. Sacha's poems form a concentric circuit in the deep structure of the book. At their best they approach the quality of Lotte Kramer's lyrical miniatures. The son's brilliance outshone the mother's in terms of primary output, but she was never in the shadow. Both spoke their minds and were the first to detect a weakness in a piece of writing or an argument of the other.

Sacha Rabinovitch's mother's mother's family were Cattaouis, members of the Cairo Jewish élite, who could trace their ancestry back thousands of years. Her maternal grandfather, a Rossi, was from Ferrara, one of many Jews whose families had been encouraged to settle in Egypt by the new Sultan in 1838. Her father was an Ashkenazi Jewish doctor from Odessa. Orphaned, she was eventually raised by her grandparents. Already deeply familiar with French and English culture, she married the brilliant but feckless Jean Josipovici in 1934. They left for France, where Gabriel was born at a dangerous moment for Jews in general, not least his mother. They made for the Dordogne where they survived until the end of the war. Abandoned by her husband she returned with her son to Egypt, arriving on his fifth birthday, 8 October 1945. There he later attended Victoria College (alumni included King Hussein and Edward Said, whose own autobiography counterpoints fascinatingly with this one). They left for England before the Suez crisis - which saw the virtual end of one of the most ancient diaspora Jewish communities.

After working at mundane jobs to support herself and her son, she later settled with him in Oxford and finally in Lewes. Among their mutual interests were pets and sports, and the long walks they took together on the Sussex Downs as often as possible. When Gabriel became a professor he seems to have done as much learning as he did teaching, for they both participated in Greek and Hebrew reading groups. In her later years Sacha made highly praised translations of difficult French and Italian books. She is buried in Hove Jewish cemetery and lives on in this beautiful book, at once moving and austere, about the interplay between character, destiny and chance. Like Walter Benjamin and other distinguished Jewish unbelievers, the couple seem to have led emblematic Jewish lives: wanderings, scholarship, language, commemoration. Unlike Benjamin, Gabriel survived the war, thanks to Sacha. It is pointless to speculate about what might have transpired had the two been 'brave' or 'normal' enough to go their separate ways. What counts is the quality of the life they lived - together in a marriage of true minds - given the choices they made. 'Whatever grace and virtue we give to others comes from our own fell needs. We pray for the face we need and call this intellectual perception.' Thus, Edward Dahlberg. Fortunately for them, and indeed for us, Gabriel Josipovici and his mother needed one another.