The first of the essays and speeches that are collected in At the Same Time is a meditation on beauty. Written during the last years of Susan Sontag's life, when she was ill with cancer, these 16 pieces brim over with vitality. Every one of them opening up fresh lines of thought, they are in no sense last words. Unlike many politically engaged writers, Sontag never hankered after the security of a finished system of thought. If she acquired a reputation for contrarian thinking it was because she responded directly to historical events, which rarely conform to ideological stereotypes.
Enraging bien-pensants when she noted that Reader's Digest gave a truer picture of communism than could be found in the journals of the left, she provoked fury on the right by observing (in a piece written just after the 9/11 attacks, included in this volume) that politics had been replaced by a kind of psychotherapy whose goal was to spare the American public from being burdened by too much reality - not least the reality of intractable conflict in the Middle East. In each case, she was speaking a truth that had been silenced by prevailing opinion.
At the Same Time is a record of Sontag's thinking in progress. Even so, the book's opening reflections on beauty undoubtedly express her lifelong beliefs - and may help unravel a persistent paradox in her life as a writer. Against the puritan tradition that suspects aesthetic values because they threaten the primacy of morality, she declares that "beauty, even amoral beauty, is never naked", for "the aesthetic is itself a quasi-moral moral project". Engaging with beauty enables a type of wisdom, she believed, that "cannot be duplicated by any other kind of a seriousness". This is a conception of beauty that recalls Plato, and Sontag is clear that modern democratic relativism - the belief that aesthetic judgement is a matter of subjective preference rather than a perception of some kind of reality - undermines the very possibility of wisdom.
Here we have one of Sontag's many departures from current liberal orthodoxy - her "elitist" insistence on the enduring importance of values that are neglected in popular culture. It is true that she had no time for the postmodern view that the cultural consumer is always right. Radical subjectivism of this sort produces a cult of fashion masquerading as irony, "the promiscuous, empty affirmations of the interesting" that places human subjectivity at the centre of the world. In contrast, she believed, beauty "reminds us of nature as such - of what lies beyond the human and the made".
Though the fact is commonly resisted, an abiding concern with aesthetic experience does not coexist easily with strong political engagement. An urgent interest in reshaping the world is at odds with the attempt to discern the beauty it contains whatever its flaws. More than any of her critics, Sontag was aware of this tension. At times she seemed wary of the moral activism that fuelled her protests against injustice, and may have regretted not giving more of her energy to writing novels. It is striking how many of the writers she admired lacked, or even scorned, political commitment. An earnest desire to improve the human lot does not figure centrally in the work of Fernando Pessoa, E M Cioran or W G Sebald - writers Sontag fervently praised and publicised. When she promoted the work of an indefatigable activist and agitator - as she does, in a luminous essay collected here, when she praises Victor Serge's neglected novel The Case of Comrade Tulayev - it was not primarily his exposure of Soviet oppression that she celebrated. It was the subtlety with which Serge pursued fictional truth in all its labyrinthine complication. Whereas an archetypal didactic "political novel" such as Arthur Koestler's Darkness at Noon sees the Stalinist era through the prism of one person's experience of oppression, Serge interweaves politics and personalities in a panoramic view of history. For Sontag, fiction was the most effective way of rendering the human actuality, and it was Serge's realistic account of the contingencies that shape human fortunes which made him the better writer.
I knew Sontag only slightly, and all too briefly, towards the end of her life. At the time she died, she was America's best-known public intellectual. To my mind, she was also the most exemplary. Intellectually and imaginatively gifted to an extraordinary degree, she used her fearless intelligence to illuminate some of the deepest contradictions of contemporary life. Her writings on interpretation, photography and illness are part of the modern cultural canon. But Sontag was much more than a critic of culture, however accomplished. Who else would note, as she does in her essay "Regarding the Torture of Others", collected here, the seamless connection between the images of torture coming out of Abu Ghraib and the clichés of the American porn industry? Or note that the photographs the soldiers posed, thumbs up, over their victims and sent to their friends illustrate a media-driven society in which everything that was once private is now shamelessly revealed? This is the moral culture that has made possible the rehabilitation of torture - a process that has taken place in a matter of a few years, but which is a defining feature of our age.
As Sontag wrote, "What formerly was segregated as pornography, as the exercise of extreme sado-masochistic longings - as in Pier Pasolini's last, near-unwatchable film Salo (1975), depicting orgies of torture in the fascist redoubt in northern Italy at the end of the Mussolini era - is now being normalised by the apostles of the new, bellicose, imperial America."
That this process should have been led by the world's pre-eminent liberal regime is also symptomatic of the times in which we live. Images of naked men stacked in heaps seem to have been sufficiently shocking to be largely withdrawn from the media. Yet practices of sensory deprivation and denial of sleep, which when practised on dissidents in the former Soviet Union were condemned as a sign of totalitarianism, are now defended by the American vice-president and his neoconservative acolytes as part of a crusade for universal freedom. One of the ethical restraints that shape civilised life has been eroded, while those responsible for the slide into barbarism rant on about human rights and the perils of moral relativism.
Contemporary politics is a surreal spectacle that few writers in any country have succeeded in capturing. If Sontag did, it was because, for her, cultural criticism and literature were not separate activities. The paradox in which she seemed at times entangled was only partly real. While moral activism does not always go with devotion to beauty or concern with truth, in Sontag's case these values served a single end. In At the Same Time we hear the voice of a unique writer, who loved the world and spent her life in an attempt to see it whole.
John Gray's next book, "Black Mass: apocalyptic religion and the death of utopia", will be published by Penguin in July