When, in 1975, Poetry Nation metamorphosed into PN Review in something like its present format, it had before it the editorial example and physical samples of the magazine Plural, published by the Mexican daily newspaper Excelsior and edited by Octavio Paz. Paz contributed to early issues of PN Review and, when censorship interrupted Plural, PN Review reported on the circumstances of the attack and on Paz's new venture, the magazine Vuelta, which did much to consolidate intellectual debate in Mexico and in Latin America as a whole. Vuelta remained curious about world literature - including poetry. Even after Paz became a national monument in 1990, awarded the Nobel Prize, he refused to turn to stone. Unpredictable, volatile, always clarifying, his essays, lectures and conversation retained that essential openness which Eliot believed an editor loses at the age of 40. His poetry kept breaking new ground - which is to say, old ground. In his later years the eighteenth century - English and French - became a favourite haunt. He died on 19 April, at the age of 84.

In PN Review 19 my version of his sequence 'Cuadrivio' appeared. A curious correspondence, preserved in the John Rylands Library, Manchester, surrounds an early version of the translation. I misread the word alcahuete (pimp) as cacahuate (peanut), adjusting the imagery to my misreading. This was, he said later, a piece of semantic twisting 'worthy of Ignatius Loyola'. No friend of the Jesuits, he wryly praised the casuistry, not the poetic skill. Though in his later years his opinions hardened, there was always about him an unaffected playfulness. In the old man the young café poet and the sceptical revolutionist survived. He never disowned his earlier selves, though he read them with harsh thoroughness. He could not have written an autobiography: the ideological vagaries of his formative years were intolerable to him.

In Valencia in 1987 I first heard him speak of George Orwell. It is Orwell whose political words and deeds the mature Paz often calls to mind: unillusion, a willingness to challenge the fashionable ideological ogres of the day. Writers had gathered in the Catalan city to mark the fiftieth anniversary of the Republican Writers' Congress and Paz's inaugural lecture was published in PN Review 59. Then in his seventies, he did not invite veneration: he seemed to court conflict. In a broadcast debate with Mario Vargas Llosa, he attacked the politician's dream of Latin American liberal democracy. Democracy depends on a critical culture, an educated electorate; Latin America possessed neither, having avoided the rigours of the Enlightenment under Spanish and Portuguese domination. Traditions of hierarchy and corruption could not be swept away, except temporarily, by European or American - or Soviet - political brooms. In a poem, he wrote of his early revolutionary fervour, 'What we wanted we wanted without innocence'. His opponents, the Europeans and academics in particular, played with politics. Nicaragua was an abstract counter in their game, where for Paz Nicaragua, like Cuba, Guatemala and Argentina, were distinct cultures, histories and, above all, peoples on whom political ideas had taken a terrible toll.

He made contrary marks on history. He acted against the excesses of his own government in 1968, at the time of the Olympic Massacre in Mexico City, renouncing his ambassadorship in India to become a focus of opposition. Twenty years before, as a Marxist, he published and analysed reports of the Soviet labour camps, turning left-wing Latin American writers - Neruda among them - virulently against him. He did not consult his own interests: he was a critic, and a critic's task is to clear space for disinterested dialogue which might lead to action. In the 1930s, he went to Yucatan to help organise schools for the sisal workers' children. His family had links with the Zapatistas and he remembered as a boy the moustached old ruffians of Zapata's army in the patio of his grandfather's house, seeking legal help and bringing edible gifts.

He found it hard not to tell the truth as he saw it. Clarity made him volatile in a world of material and political interests: he was not in anybody's pay. His imagination was Mexican, but also European. Translating poems from his collection Pasado en Claro, I commented on what seemed echoes of Valéry. They were, he showed me, echoes of Alexander Pope: embedded in the lines were phrases and closures drawn from Pope. Wordsworth affected his personal poems. He brought unanticipated tonalities into Spanish and many English and American poets benefited from his example.

Mexico lost a tribe of writers on 19 April. Paz was many poets, from the radical experimentalist to the autobiographer and confessional writer. A social critic, his work went through several phases of integrity. Unlike Orwell, he had a developed interest in the erotic and devised verse and prose styles for dealing with it. Philosopher, translator, essayist and brilliant editor, he was urgently alive in and to his time. He never stood, or wished to stand, on his dignity.