By 1974, aged 33, Michael Hartnett had already built a considerable reputation as a poet in English and was widely accepted as a genuine talent. Then, unexpectedly and abruptly, on June 4th, from the stage of the Peacock Theatre, in Dublin, he announced that he proposed to abandon English and from then on write and publish only in Irish.

It was, in the eyes of many, a quixotic gesture. Hartnett was not a native speaker, although his grandmother, to whom he had been more or less fostered out as a child, was reared with Irish and would speak it at night to her neighbours when they gathered in. Hartnett often spoke later of listening from his bed to these voices that murmured, it seemed to him, from a vanishing world.

Pat Walsh’s book revolves around that pronouncement from the Peacock stage, ranging backwards and forwards through Hartnett’s life to examine his context and formation, attempting to arrive at a summary judgment of the poet’s life and writings, returning always to what he sees as the pivotal event in both life and work.

If Hartnett expected a big reaction to his grand gesture, he must have been disappointed. Some were bemused and puzzled, others inexplicably irritated, even hostile. Most, perhaps unsurprisingly, were indifferent. Walsh is good on these reactions: he records them in all their variety, so opening fertile ground for future scholars not just of Hartnett but of our troubled relationship with our native Gaelic tongue.

Hartnett’s election for Irish was essentially private, but, inadvertently or otherwise, by making his choice, and by making a public occasion of declaring his choice, he backed into a still unresolved politics, drawing attention to a psychic wound that has never healed, may indeed never heal. By opting to write in Irish, Hartnett found himself more or less forced into polemic.

The general understanding now, and Walsh does not challenge this understanding, is that Hartnett made his choice as a gesture towards the politics of language and race. More precisely, there are many who still believe that there was a certain level of wayward atavism in his choice, that he was expressing a wilful, retrograde loyalty to a submerged Gaelic order, to a repressed and oppressed dead culture as embodied in its language.

On the face of it, Hartnett himself seems to offer evidence for this case. A Farewell to English, announced as his last book in that language, is riddled with attitude-striking, with the ventriloquised anger of the 18th-century dispossessed. Even his poems excoriating our modern lack of vision could be read as projected forward from the values of that spurned Gaelic matrix. Reviews ranged from the gentle but sceptical (Eiléan Ní Chuilleanáin) to the downright merciless and dismissive (Ciaran Carson), and Walsh does us a further service by gathering in so many of these first reactions. But, taken all in all, under and inside the protective rhetorical arguments of A Farewell to English, there is a genuine poetic impulse. What most commentators seem to miss, Walsh among them, is that Hartnett did not choose Irish: Irish chose him.

Michael Hartnett believed, very simply, that a poet is born, not made. Around his person there seemed to be always a certain psychic disturbance, giving rise to a feeling reported by many that there was something otherworldly about him. His grandmother saw it early. Equally, for all their meticulous craftiness and word-wizardry, there has always been in the best of his poems a sense of an otherwhere, as if he travelled between the world we say we know and some other contiguous but veiled reality. This, I believe, is the key not just to his character but to his poems.

There is something otherworldly, in several senses, about the first section of A Farewell to English, the title poem of the collection. Hartnett is sitting quietly in a bar when, unbidden, “like grey slabs of slate breaking from / an ancient quarry”, the words come tumbling into his mind: “mánla, séimh, dubhfholtach, álainn, caoin ...”

He is honest enough to ask “what was I doing with these foreign words?”, but his sense of poetic honour compels him to follow the summons, to allow the imperative to have its way. The poem begins to speak itself, the lost language puts him faoi geasa, he has no alternative but to accede. Everything else follows.

Hartnett, we must allow, knew what he was about; it was his business to follow where summoned. Many years later, long since returned to English, he would utter a plaintive cry: “I have poems to hand, it’s words I cannot find.” Not long after that, and not long before his death, walking one night on Dartmouth Square, when I gently suggested he was killing himself with drink, he fixed a cold eye on me and said, simply and finally: “My poems are written.”

A Rebel Act is an act of love, a book that surveys the life and achievements of Michael Hartnett with a workmanlike attention to detail. Pat Walsh has opened the ground, and done a good job of it. Neither full biography nor comprehensive exegesis, his book is a loving and valuable homage to a great poet. Nevertheless, to understand Hartnett there is no alternative to studying the poems, and studying the poems to remember: we do not write the poems; the poems write us.