WHEN Susan Sontag died in late 2004, the English-speaking world lost its pre-eminent female intellectual. The American writer was at ease with her own seriousness of mind and her role as a 'public' intellectual . . . which not only influenced her, but was in her genes.

She believed it was both her right, given the gift of a worldclass intelligence (she was reading Goethe by the age of 10), and her duty to put forth ideas. But her final months were tormented by the fact that an imperious and courageous passion for comment and activism had distracted from what she most wanted to do: write fiction.

Only fiction gave her pleasure as a writer. The essays and polemics were an "evangelical incentive". After postgraduate work at Harvard, Oxford and the Sorbonne, her literary career began with a novel, The Benefactor, published in 1963. She wrote three others, winning late popular success in 1992 with her final one, The Volcano Lover. By then her always challenging, often controversial canon of nonfiction had won her a stellar reputation and any number of awards, honours and fellowships.

But they were not enough.

In his forward to At The Same Time, a collection of 16 essays and addresses written in the final years of her life, Sontag's son David Rieff regrets that her last major work was another essay.

'Regarding The Torture Of Others' is a meditation on the supremely contaminating nature of the Abu Ghraib photographs.

The motors of Sontag's commentaries are her moral and aesthetic perceptions and both have seldom been more devastatingly deployed. Yet Rieff, wistful for her mislaid ambitions, writes: "I wish, well, I wish she had written a short story."

The so-called Dark Lady of New York intellectual life . . . a majestic presence with handsome looks, compelling eyes and dramatic hair . . . was a formidable critic of US foreign policy over four decades, from Vietnam to Iraq. But she was no armchair critic. In 1968, she visited Hanoi and published 'Trip To Hanoi'.

She lived in Sarajevo for several months during its three-year siege by the Yugoslav National Army and directed a production of Waiting For Godot in a candlelit cellar. Such was her originality of thought and ability to argue every issue on its merits or demerits that she never became a figurehead for fellow travellers.

She angered both right and left.

"She ran received opinion through the shredder and looked at things again, " said Margaret Atwood after Sontag's death.

She even angered feminist writers. It almost goes without saying that, by instinct, intellect and practice, Sontag was a feminist. In 1952, aged 17, she married Philip Rieff, her sociology lecturer at the University of Chicago, 10 days after they met.

Six years later when she divorced him, she refused his offers of child support or alimony. For her, female emancipation was a given, even if one imperfectly achieved.

In 'A Few Weeks After', a response to questions on 9/11 put by an Italian journalist and published here in English for the first time, she states: "What those who perpetrated the slaughter of September 11th were trying to achieve was not the righting of the wrongs done to the Palestinian people, or the suffering of people in most of the Muslim world. The attack was real. It was an attack on modernity (the only culture that makes possible the emancipation of women) and, yes, capitalism."

But she upset feminists by refusing to nail her colours to their ideological mast, just as she dismayed the gay community by refusing to allow her bisexuality to be used as propaganda in the gay liberation movement. She never made public her romantic relationship with photographer Annie Leibovitz but in later years she cheerfully acknowledged her bisexuality. In an article in the Guardian in 2000, she remarked that she had been in love nine times. "Five women, four men."

Was it her "duty", according to her definition of intellectual responsibility, to resist being corralled in to any ideological ghetto? Ironically, the American writer with the most comparable intellect mounted the most forceful attack on her failure to march with the sisterhood. Camille Paglia famously argued that Sontag's "cool exile" from the women's movement at a time when it was dominated by lesser brainboxes . . . Gloria Steinem, Kate Millet, Germaine Greer and their like . . . disastrously undermined its credibility. "No patriarchal villains held Sontag back; her failures are her own."

But Sontag hated provincialisms and insisted that, if she had to live in the US, she could live only in Manhattan "because it's full of foreigners". Outside the American cities, she added, "the rest is just drive-through". So perhaps, with feminist ideology:

outside the core arguments for women's emancipation the rest is just drive-through.

This collection may not be the best example of Sontag's work but it covers the spectrum of her preoccupations, from ethical and aesthetic reasoning to literary analysis to political comment.

More than anything, however, it returns to scrutinising the potency of words . . . and how their power can cause or prevent action. Few have used words with more care and, although the more abstract reflections of her prose are demanding, they must be cherished in a world where, increasingly, the written word is represented by sloppy, semiliterate blogs and breaking-news captions.