[In the following essay, Gilbert discusses Sontag's writings on cancer and AIDS, using interview quotes to illustrate the author's opinions and confusion surrounding the social implications involved with these diseases.]

Like Woody Allen in Zelig, Susan Sontag appears to have been there, boots planted centre-stage, at every cultural high spot of the last quarter-century: the “youth movement” of the 1960s; opposition to the Vietnam war; feminism; anti-censorship … Aptly enough, she even popped up in Zelig itself.

This week, she has been in London raising money for Aids, an event centred on the re-publication of her New Yorker story “The Way We Live Now”—about a network of friends, of whom one is in hospital with Aids—in book form, with lithograph illustrations by Howard Hodgkin, the Turner Prize-winning British artist. In a gap between readings, fund-raising dinners and interviews, I met Susan Sontag in her Soho hotel and asked her how this “campaigning” persona clashed with her other existence, as one of our era's most complex and subtle analysts.

Her answer was swift: she has never been a campaigner. “The amount that I do is vastly exaggerated. I mean, what's the last political statement I made? I organised the American writers' response to the fatwa against Salman Rushdie. Since then I haven't opened my mouth.”

The last should not be taken literally. Sontag speaks fluently and likes to speak. Both language and ideas give her so much palpable pleasure that you feel that, were strangers to accost her in the street, she would want to answer whatever they asked. This explains why she may under-estimate the number of platforms on which she has stood; but it also explains why people exaggerate her presence in the public arena. Not only is she mesmerising, with great intellectual and physical grace; but her mixture of thoughtfulness, mercury awareness and non-stop internal argument continues to echo long after the voice has stopped.

Writing, however, is what she does. “I really try to convey what I think in a way that has pockets, you know; that does acknowledge the complexity. That's why I don't generally like to do television. When I'm talking, I can't remember all the different sides of it. But then, when I write … it's a kind of layering process. You know, I lay down one layer and then I lay down another layer and then that sort of modifies the first thing, and then I get something that seems not too simple and seems eloquent and seems powerful and that's the argument that I want to make: one that one might want to re-read; not one that one would want to summarise and say, ‘Oh, I know what she thinks about this, she's against it, she's for it.’”

The problem is that Sontag bestrides a crossroads where art, academe, politics and street-life converge. She is therefore particularly vulnerable to having her feet run over. In her youth, fellow academics accused her of debasing critical writing by using its rigour to examine popular culture. Now she is charged that AIDS and Its Metaphors, the non-fiction book she wrote after “The Way We Live Now”, could reduce the pressure for action on Aids by its calm assurance that a cure will be found, and its undermining of the metaphors by which the syndrome is made into something more portentous than an illness.

“Oh, that's absurd,” said Sontag. “What else could it be but an illness? Even if it were some of the things that people act as if it were, if it were a state of mind, if it were a symptom of social disorder or moral degeneracy, would that make it more imperative to do something about it? Oh, you know, it's so … I often have the feeling that people don't really read what you write. I mean, there's all sorts of arguments in the book to try to understand why people need to use these metaphors.”

“The Way We Live Now” was also written, in part, to help in understanding: what Sontag describes as “an education of the heart”. It does this by weaving a lattice of voices expressing the pain, fear, compassion and euphoria (Sontag refuses to ignore this last) that greet the arrival of probable death within a close-knit community. The comfort that it offers is an artist's: not the comfort of meaning but of shape. This does not, however, make either it or its need less emotionally real.

The story's catalyst was the news that Sontag's friend Robert Mapplethorpe, the photographer, was in hospital. She wrote it fast, and talks about it now as a “kind of premonition”, Mapplethorpe being the first of 30 close friends in whose death from Aids she has since been involved. However, as with the non-fiction book that she wrote about her cancer, Illness as Metaphor, the personal experience at once rippled out to form a larger, more general statement, thus feeding into the criticism that Sontag is distanced, uncommitted.

In a study of Sontag published last year, Sohnya Sayres points particularly to a passage in AIDS and Its Metaphors where Sontag writes that fear of Aids has enforced “a much more moderate exercise of appetite”. Sayres reads this as approval, a sign of Sontag's ever-increasing “conservatism”. The truth is less straightforward.

“I start absolutely by assuming that what is desirable is a pluralistic society, a society that does not impede a number of ways of being and feeling, and that includes different kinds of sexual relations. So, in that sense, I couldn't possibly be censorious about sexual experimentation. But, on the other hand—there's always another hand—I've lived long enough to see become publicly acceptable extremely cynical and callous ideas about personal relations, about sexuality.”

As illustration, Sontag cited such films as The Silence of the Lambs and David Lynch's Wild at Heart, the second of which she has been appalled to hear described as a “charming comedy”. “I wear turtle-neck sweaters when I go to the movies, so that I can pull the thing over my head, and I turn around and everyone's sitting there, not even blinking; so I mean, there is a kind of mutation of feeling and a rise in the tolerance for brutality.” The crucial point, however, is this: when I asked her whether this “tolerance” was growing in real as well as in representational life, she looked for a moment surprised that there might be a difference. Similarly, when I asked her whether she felt moral conflict about raising funds, some part of which could be paying for experiments on chimpanzees, she sounded sincerely perplexed. “I don't know what to say. I'm horrified by cruelty to animals and all the examples of unnecessary use of animals in laboratories, and I don't know what the practical consequences of disapproving of it so much … I don't know whether one should want not to use animals, if it could mean finding proper treatment earlier. I just don't know … I don't know how to think about it.”

“Practical consequences” ought, perhaps, to be marginally better considered. But then, as she said, Sontag is not a campaigner. She is a public figure whom we still desperately need: someone for whom imagining, thinking, saying and feeling are indivisible. If some of us know more clearly where we “stand” on, for example, vivisection, we should also know the ambivalence that we trampled in order to get there. As much as political positions, or more so, contradictions need a guardian.