Among the manuscripts on show at the Mallarme centenary exhibition, held at the Musee d'Orsay in 1998, was a bundle of 202 little squares of notepaper, scrawled over in barely legible pencil. The startlingly small size of the paper, and the almost furtive nature of the scrawl - so unlike Mallarme's usual impeccable script - was instantly arresting. For this was the manuscript of his projected poem (or prose piece, or drama, it is never entirely clear) for his son Anatole, who died of rheumatic fever in 1879 at the age of eight. As if in keeping with the secretive look of the manuscript, the poet never mentioned these notes in his correspondence. The public Mallarme was engaged upon his mysterious oeuvre, his impossibly ambitious attempt to render in words the "orphic explanation of the earth". But in private, for many months after his boy's death, he was engaged on a project closer to home, the "Tombeau d'Anatole", which was never completed, or even given an official title. In fact, the manuscript only came to the notice of the general public in 1961, with the publication of Jean-Pierre Richard's magisterial edition from Le Seuil.

The death of a beloved child is perhaps the most difficult, and yet most tempting, poetic subject of them all. But what if the child is your own? Shelley, stricken after the death of his son William, could only manage a fragment or two. For a beloved friend, rather than his own child, Tennyson wrote In Memoriam, which Mallarme described, disbelievingly but admiringly, as "a whole cemetery for a single death". Victor Hugo, commemorating the death of his daughter Adele, composed one or two of the most moving lyrics in all French poetry. According to his daughter Genevieve, Mallarme once confided that he envied Hugo's ability to write of his child's death, adding "cela m'est impossible". The notes that make up Pour un Tombeau d'Anatole are what remain of his attempt to do so, and in the words of Patrick McGuinness - who has now provided a fine new translation of it - the text "seems at once a foundation and a ruin". For admirers of Mallarme, it is also a moving document, so different in kind from his published work, chiefly because, as the poet's chief exegete Jean-Pierre Richard says, "la chose a dire l'emporte sur la maniere dont il la dit". Not that Mallarme was a stranger to elegy; his Hommages et tombeaux to Gautier, Baudelaire, Poe and others stand among his most impressive works. In these, he writes with the assurance that poets, by their legacy of words, leap over death. In the case of his own little son, he was not so sure.

To come to terms with the full import of Mallarme's apparent failure to fashion a coherent whole out of these splinters of naked thought and feeling it is worth remembering that he had already rigorously denied himself any of the usual consolations, religious or transcendent, that lay to hand. In his great letters of 1866, written during a period known as the "Crise de Tournon", he had come to a position philosophically approaching Nietzsche's.

God is dead, and language a mere system of arbitrary signs overarching the void.

Human beings were mere substance, "de vaines formes de la matiere". It was on this void that he then constructed his Platonic idea, "la notion pure", that language, indeed single words, could evoke the essences of things, essences retaining no emotional attachment to those things, but existing rather in a parallel universe with its own laws. It is this idealizing tendency in the poet, graphically termed "excarnation" by Yves Bonnefoy, which was to be so acutely challenged by the very real death of his own flesh and blood.

Mallarme is the first to recognize this, as many of these fragments show - "or: ordinary Poem / It is true - you have struck me and you have chosen your wound well - / etc, - but / - ----and vengeance struggle of a spirit and of death". In a letter to Robert de Montesquiou, Mallarme used another striking image: "Je ne croyais pas cette fleche terrible dirigee sur moi de quelque coin d'ombre indiscernable". In the dynamic of the text as we have it, one of the most far-reaching themes is precisely this struggle between father and son: "struggle of the two father and son the one to preserve son in thought - ideal -the other to live, rising up etc; - ". There is a concomitant, and terrible because never admitted, struggle between the father and the mother (designated simply as "Mere" and "Pere" throughout). The father qua poet tries to spiritualize the fact of death, or its likelihood (since the projected first part of the text was situated before the boy's physical death) - and thereby somehow guiltily predicts it, or even hastens it, while the mother, essentially in denial, clings, by her tending, to his physical survival.

A second major theme that emerges is that of filial succession, now unnaturally broken; in this Mallarme again owns up to fears and guilts of his own. While he apparently looked upon the boy as his literary successor, who would bring his great work to completion - "father who born in a bad time - had prepared for son -a sublime task" - he also acknowledges the physical weakness in himself that Anatole, fatally, inherited. Hence, more guilt.

Nor should we be blind to the ordinariness of several passages, which attest to the text's authenticity, and add to its value as a human document. Exclamations like "no one can die with such eyes" or "to find absence only - / - in presence of little clothes - etc. - mother". Or this, somehow unbearably bleak: "true bereavement in the apartment - furniture - not cemetery - ". The death of Anatole would seem to confirm the poet's apprehension of "le neant" and at the same time, because the brute fact of it strikes so at his human heart, renders his word-making, spiritualizing instinct suspect. It is nature's revenge on philosophical hubris - "nous ne sommes que de vaines formes de la matiere".

Unfinished as it is, this text, so ably presented by McGuinness, seems to me an indispensable part of Mallarme's oeuvre. It is the cruel counter-thrust that leaves the poet inconsolable, but refusing still to take some illusory balm to his breast. What is left us is his "fury against the formless".