This unsettling feeling turned out not to be merely personal. It is, to some extent, generational. And, more importantly, it is also political. Something that may seem extraordinarily naïve - how can you not know you are a woman until you are 30? - is, in fact, a direct result of our liberation. It should not come as a surprise, for example, that recent books such as Naomi Wolf's Misconceptions and Rachel Cusk's A Life's Work have seen motherhood as a radicalising experience. Because although that may sound like old-fashioned chauvinism - women imprisoned by their sex or by that gender stereotype, the 'maternal instinct' - it is a long-term effect of 1970s feminism: we are mostly now not imprisoned by much until then.
We know that women are having children later now. But the issue here is not simply that the realisation that we are not the same as men comes to women of my generation much later in life than it did to our mothers; to many, it also comes as a shock. Sara Singer Schiff, a 30-year-old editor at a women's website, believed until recently that women had 'made it'. Yet when she started to think about having children, she says she was 'genuinely shocked to discover that, on this issue, I was no different from women and mothers through time immemorial. I was bound to my biology in a way that I had never previously been aware of.' It seems that, until a certain point, most women think of themselves as people, plain and simple, and have no reason to dwell on what Marina Warner calls 'the enterprise of living as a woman'.
What I am describing is less to do with actual motherhood than the consideration of it, and it is more broadly to do with self-image. Many of the women I have spoken to don't have children and don't know if they can or will have them. So the problem is more personal than the practical issues of childcare and employment. It is something like what Germaine Greer observed a few years ago: 'Where women were once nothing but reproductive organs,' Greer wrote, 'they may now claim no specifically female organs and no specifically female functions. The 1969 female eunuch was nothing but a womb; the 1997 woman eunuch has no womb.' The result of 'liberation', for many women, has been to act in spite of, rather than in collusion with, our physical selves.
Natasha Walter has advised us to do away with the old feminist adage - 'the personal is the political' - since the political, she believes, gains strength by shedding the baggage of the personal. It's a persuasive argument, since there is still so much work to be done: on matters of equal pay, equal rights and better childcare, the battles are clearly not over. But in an age when eating disorders are on the increase, when women feel even more pressure both to succeed and look beautiful, when the problems of balancing work and domestic life have, according to one feminist, actually become worse than ever, the personal can't be left in the lurch. A number of the women I have spoken to have felt guilty for dwelling on these issues. But they are not complaining; they are successful, and bewildered. And their private unease is so pervasive that, together, they form a collective voice that deserves to be heard.
Because whatever the changes in women's public lives, the issues of our private lives remain much the same. Your beliefs about sexual equality don't prevent you from feeling ambivalent about your appearance or insecure about your intelligence. Your ambitions for your career may sit uneasily with your desire to have a child. In other words, though the personal may be seen as having a political reach, the political doesn't always impinge on the personal as much as many of us hope it might. As Germaine Greer has put it: 'Equality legislation cannot give me the right to be at ease in my woman's body.'
Feminism has made so much progress on the surface that what it had to say about our personal lives has been all but forgotten. We don't need to separate the personal from the political. We need to rescue the personal and make it political again. Feminist historian Sally Alexander has said of her Seventies activism that 'our actions were about self-discovery as well as imagining a better world'. Both of these projects went hand in hand, and they should go together now. We don't need a new feminism that gives us equality at work and leaves our private selves in crisis. We need the old feminism back, not out of an unproductive sense of nostalgia, and not because we fail to appreciate what has already been done, but so that we can harness both aspects of it for a new age.
Many women of my generation feel they have missed the boat on the great political movements of the twentieth century. As one woman I spoke to put it: 'I wish I'd been born in an age when there was something more concrete to fight for.' In fact, there are things to fight for - we still can be feminists - but because of the period when we were born, we don't necessarily start out that way. I have often thought about the first tutorial I had at university on the subject of feminism.
Two of us arrived, armed with our copies of New Feminist Criticism, expecting to be asked to think about literature with a feminist slant. But instead, our tutor, an energetic and inspiring woman, told us what was wrong with women's lives. She spoke about childcare and detailed some of her partner's less charming domestic habits. She said it was generally men who had affairs, because if there was any commuting to be done, the man generally did it. I interrupted to say my mother commuted to work. 'OK,' she said, 'your mother's the exception. But, for example, women mostly do the cooking.'
My friend interrupted to say that her father did all the cooking in their house. 'Right,' she said, 'so your father's the exception.' After a few more of these exchanges, the tutor became exasperated, and gave up. 'Uch!' she said, as if about to spit out the dirtiest of words, 'you're post-feminists!'
We didn't mean to be, of course. We had arrived hoping to learn more about what feminism was, or had been, before the 'post' kicked in. But clearly we were born in an era that made us 'post-feminists' chronologically, if not by choice. I was born a year after Sexual Politics was published, the year of the first women's liberation demonstration in Britain, the year The Female Eunuch came out in paperback. That edition carried on its cover an image that has now become an icon - a suit of flesh, hanging up to dry, airing out the old assumptions about what a woman was supposed to be. We had been oppressively reduced to the sum of our body parts, the image said, and it also implied that a gender stereotype was something put on you, like an item of clothing; there was a liberation in the idea that you could take it off. I could not, of course, have made sense of it then, and that is the point about where my generation falls in relation to these politics. We can call ourselves feminists, but we cannot claim to have had any part in the battles that liberated us. We are beneficiaries of a movement that 'is no longer a movement', as Sally Alexander has said.
And, beyond the mere chance of timing, my university friend and I were, whether we were conscious of it or not, 'post-feminists' ideologically, too. Our age had had an effect on our ideas. The late critic Lorna Sage pointed out that feminists rebelled against their mothers more than they did against their fathers: 'You aim your feminism less at men,' she wrote, 'than at the picture of the woman you don't want to be, the enemy within.' When we were growing up, our mothers didn't provide such negative role models - we didn't necessarily define ourselves against them.
'You'll see,' the tutor kept telling us, 'when you start working, or living with someone, or having children - you'll see that it's not the way you think it is.' We thought she was wrong, and that the times she predicted we would one day encounter had in fact passed, long ago. But I have had cause to revisit that moment since then, with every sexist word that is addressed to me. And that is why, for me and for many others, post-feminism is something you grow out of, in order to become a feminist.
It is 52 years since Simone de Beauvoir famously wrote that one is not born a woman but becomes one. In that time, we have been taught that we needn't just become women because, as de Beauvoir suggested, culture constructs us that way - we can also choose to become women, however we want. We can each arrive at our own definition of what a woman is. If anything, however, the apparent array of choices available to us can make living as a woman more confusing. Sheila Rowbotham, a pioneer of second-wave feminism, has admitted that 'none of it is as simple as we thought back then'. Natasha Walter, author of The New Feminism, now points out that 'feminism hasn't made things harder, but it does mean we have to make choices our grandmothers didn't have to make, and I think we have to be honest about that'.
Few things are as they seem. Sexism, masked by political correctness, is more insidious now and more difficult to attack. Yet its presence is surprisingly strong - one black woman I spoke to said she had encountered sexism earlier than she had encountered racism and a gay woman said she came across sexism more often than homophobia. In many ways, what are presented to women as options are really new demands; professionally, many women still operate as if they were men. At home, many women do most of the childcare and most of the housework.In a number of cases, 'having it all' simply turns out to mean doing it all. So it would seem that we are not choosing to 'become' women; we are just muddling through.
The women I have spoken to on this subject have fallen, with startling consistency, into three groups, depending on their age. Those in their mid-twenties seem extremely confident and have, for the most part, interpreted my questions in relation to their professional life. Some of them have the added, arguably reactionary, desire for men to open more doors for them and catch spiders more often. 'I haven't reached the point where I have found that my sex has impeded my actions,' says Lauren, a 25-year-old editorial assistant at a dotcom magazine.
Jessica, a 23-year-old management consultant, says: 'I can't honestly say I feel like I've encountered any discrimination along the road to where I am today. I have no complaints. I act as a professional and expect to be treated as one - end of story.'
'I have been brought up to be strong and independent and to think that I am equal if not better than men at all things,' says Farrah, 24. 'However,' she goes on, 'I still like it when a guy takes me out for dinner or opens a door. Is this bad? If a man is being a gentleman, does it mean that I am inferior or weaker?'
The women who are about 30 have hit the turning point I am attempting to describe. 'I've realised a few things in the last couple of years,' says Georgina Pye, a 31 year-old television producer. 'And the troubling thing is that they're all a bit contradictory. Having spent most of my life thinking that my mum was a great role model because she'd retrained in a difficult profession in her thirties and become really successful, I now look at her life and the thing I envy most is that she had loads of kids when she was in her twenties and is still young now I'm grown up.
'I suppose I don't really know anymore how to define success. I still want to believe that everything is possible but I'm coming to think that everything probably isn't and that I actually have to make positive choices about which things are the important ones.'
'I think many modern women don't imagine themselves as such, but rather as sexless beings, or even as "men",' says Kathleen, a 28-year-old who works in politics. 'It's a great shame because it's really about women adapting ourselves for success in the male model of the world, where it is men who hold power. Being a woman only begins to make a really substantive difference to someone like me, who otherwise has a career like any man I know, when I have children. And I think that well-educated women today are really quite unprepared for this. Being unprepared means we're not very ready or able to work against it.'
Tess McPherson, a 29-year-old doctor with a two-year-old daughter, confirms that, when she was growing up, 'the complexities of the choices that women have to make weren't really addressed. 'My mum had had to face quite a lot of barriers to become a doctor but because she had done it and had a family, I assumed it was easy. And it has been easy, in a way, because I think there are fewer stereotypes. The barriers left are much more subtle, though, and probably more difficult to deal with than a full-on old-boys' network, because whereas the generations before us had to battle with men who thought they couldn't do it and prove themselves to them, we have to battle with our own confusions. Having had my daughter doesn't really clarify things but just confuses them more - because I want to both do well in my career and be a good mum, and making decisions about how to achieve this is not easy or obvious.'
The older women I spoke to, mothers in their mid-thirties, have seen quite clearly how the battle of the sexes pans out at home and at work. Of all the women I interviewed, they are the most disappointed. Sophie Finzi, a writer, expresses it best: 'When you have kids your whole relationship to sexual politics changes. There have been times when I have leaned down to pick up a discarded item of clothing and thought, "I didn't expect this. My mother didn't want me to do this and that is why it was kept from me that I would have to do this." I have sworn that I will not let my daughter have to do so much. That for her it must be fairer, with less responsibility heaped on her shoulders.'
When you hear these women's comments, they show a striking progression - from the apparently free and post-feminist 24-year-old to the bewildered 30-year-old trying to adapt to a new reality, to the re-politicised woman in her mid-thirties. None of these women is old enough to have been a part of feminism's Seventies heyday. And yet gradually, they are returning to issues that were voiced in that era. This pattern is diametrically opposed to the old cliché of the student revolutionary who becomes more conservative as he ages. These women are more likely to call themselves feminists the older they get. Why? Because the difficulties appear only to increase, and we badly need to look at those old arguments again.
When I asked Lynne Segal, professor of gender studies at Birkbeck College and a former second-wave activist, whether she thought there were aspects of feminism that needed to be revived, she replied: 'Yes. The basic practical agenda of trying to make home lives and working lives more compatible, which is one place we began - that situation has got worse. More women are in jobs and they are more autonomous - that's better. More attention to violence - that's better. But the basic practical problems are not solved.'
On the more personal issues, she believes that 'rethinking what it is to be a woman, and so on, has not yet been able to generate differing images of healthy and attractive womanhood'. Culture still pressurises and constructs us along very familiar lines. 'And so,' Segal concludes, 'everything needs to be revived, but revived in ways in which women aren't situated as victims.'
Sheila Rowbotham, reflecting recently reflected on her activism of the early 1970s, commented: 'Everyone was saying the big problem in the future was going to be too much leisure. Instead, here we are in the labour force, working longer hours, suffering from stress... well, something went wrong. There should be more to life than having no time to live.'
There is more - the world of work is not enough; the political must never leave the personal behind. And if only we can redefine it for ourselves, feminism can help us get our lives back.
Some names in this article have been changed
Women in a man's world
Sophie Finzi, writer, 37
Having kids changes your whole relationship to sexual politics. In my first marriage, our genders seemed almost interchangeable before my son was born. Then it took us both by surprise that I was so maternal and soft and he became rather gruff and paternalistic. He resented having to bring in the money and I resented doing all the home and baby stuff. I don't know a single couple in which the woman's brain is not filled with packed lunches and socks and egg-boxes while the man is able to turn his brain to anything he likes. Recently, I couldn't sleep after reading Martin Amis's autobiography. He and his father made writing seem to be a man's thing - creative thought unhindered by the mundanities of domestic life. A writer like Amis has so much clear time - hours and hours each day even though he has children. That time is his because there've always been doting women doing things around him. I found it very disturbing.
Vivienne Francis, film executive, 30
I always assumed I'd be successful - my parents (typically African) were obsessed by education. I did maths at university and loved it. I had daydreamed my perfect life. Lovely smart house, boyfriend; I'd go to the theatre a lot, I'd be the first or the youngest or something. Big office, youngest MD... I got a rude awakening. I did a couple of corporate finance jobs in the City and found the office environments overwhelmingly male, and I felt threatened. For the first time in my life I was conscious of being a woman and black. I decided I didn't have it in me to fight that battle, so I got a job in fashion and entertainment PR before ending up in film. I'm very mixed up about children and marriage. I really want those things but I'm too selfish, too career-minded, to have children now. I can't stand how mushy some women become once they have kids. I often think (and I hate myself for this), what if I didn't like my children, if they didn't live up to my expectations?
Jessica Watters, management consultant, 23
Growing up, I always thought I could do anything I wanted professionally. It was never an issue. On the personal side, there are a few problems. I find myself apologising for, and justifying the fact that I want to get married and have children one day - like this is just too traditional. The person I get this most from is my mother, who still holds out hopes that I'll grow up to be a virgin doctor with no need for men or romance! I'm sure a lot of people my age can identify with their mothers not wanting them to get stuck in the 'trap' they feel they're in.
1949 The Second Sex by Simone de Beauvoir.
1961 The Pill became available in Britain.
1967 The Abortion Act allowed a termination when two doctors believed that continuing the pregnancy would be a risk physically or mentally to the woman.
1970 The Female Eunuch by Germaine Greer helped mobilise the women's movement and turned Greer into one of the most important voices in feminism.
1973 Fear of Flying by Erica Jong, described by Henry Miller as 'a female Tropic of Cancer '.
1975 The Sex Discrimination Act and The Equal Pay Act came into effect, making it unlawful to offer different pay and conditions where women and men did the same or similar work.
1990 The Beauty Myth by Naomi Wolf took on the beauty industry.
1992 Backlash: The Undeclared War Against Women by Susan Faludi analysed the way the mass media works against women.
1992 Our Treacherous Hearts by Ros Coward argued that feminism had achieved all it set out to achieve.
2001 The morning-after pill became available over the counter.