What is feminism? "Simply the belief that women should be as free as men . . . Are you a feminist? Hahaha. Of course you are."

Caitlin Moran's How to be a Woman is firm, delightfully firm, on many things – heels (against), pubic waxing (against), abortion (for), the disadvantages of economising on sanitary products – and she is firm, she insists on, this simple definition of feminism. Feminism is just equality. Would a man be allowed to do it? Then so should you. Would a man feel bad about it? No? Then nor should you. Everything else – the pressure to be sisterly ("When did feminism become confused with Buddhism?"); the idea that we should be held to account, as feminists, for every possible ill that could befall the modern woman ("There's a whole generation of people who've confused 'feminism' with 'anything to do with women'") – all of that is just hassle in disguise.

Moran is right, it is simple: and yet, for such a simple message, its cultural penetration has been patchy, fluctuating and disappointing. People who like to sound the death knell for the ideology – it's remarkable even that such people still exist – point to the fact that young women tend not to describe themselves as feminists. There is a certain sour enjoyment from pointing out all the privileges that they owe to the sisterhood – the equal pay, the maternity leave – but I would query the importance of the self-description. One can promulgate the values of feminism quite effectively by just living them, by expecting fairness at work and at home, and young women are better at this, less surrendered, than anyone. Much more chilling for me was the recent debate around the Slut Walks. On mainstream television (Newsnight) the Conservative MP Louise Bagshawe said that the word "slut" could never be reclaimed, would always be a horrible word, because it "lionised promiscuity". Meanwhile, in mainstream print (the Sunday Times), columnist Minette Marrin wrote: "There is no universal human right to dress and behave like a sluttish streetwalker touting for sex, without occasionally being taken for one." These are not young women; they have been many years in this culture, without apparently encountering feminism's basic precepts. It ought to be taken as given, by now, that you can object to promiscuity generally, if you like, and I imagine this would be on faith grounds, but if you object to promiscuity in women, specifically, then you are barking up the wrong skirt. It ought to be obvious, beyond remarking, that a woman should be able to sleep with whom she wants, when she wants, as often as she wants, without danger and without shame. It surely should go without saying that being a prostitute and being raped are two different activities. The fact that so little progress has been made in the specific area of female sexuality is partly because of divisions within feminism – many of the boldest voices see the Slut business as a post-modern stunt, where sexual violence is used as a stalking horse to co-opt young women into hot pants and thence into the raunch culture that oppresses them further. Sylvia Walby, in her new book, The Future of Feminism, adjudicates on this magisterially. But divisions alone cannot account for this.

The best explanation I have read comes from Walby's account of the relevant "epistemic community", a term which is defined by Peter Haas as "a network of professionals with recognised expertise and competence in a particular domain . . . who have 1) a shared set of normative and principled beliefs . . . 2) shared causal beliefs, which are derived from their analysis . . . 3) a shared notion of validity and 4) a common policy enterprise". Such a community is the means by which ideas become practices and norms. The patriarchy isn't going to smash itself, to paraphrase Habermas (sort of), but nor is it so entrenched that it cannot be overturned by sustained, informed argumentation. This accounts for the huge advances that feminism has made – consider the daunting economic inequality that has been tackled in the past four decades, the astonishing speed of equal pay legislation across Europe and indeed the world. But it also accounts for the relatively meagre differences wrought in the arena of sexuality, because the epistemic community isn't there, the argument was never sustained. The last person to make any serious noise about female sexuality was Shere Hite; that was nearly 35 years ago. Orgasms were the stuff of the academy and of politics in the 1970s, but now, to go anywhere near that stuff would be a fast and effective way to sound like a crank.

I was expecting to find some tension between the dual purposes of memoir and polemic in Moran's book, but in fact, every word of the memoir is loaded with political importance. Female sexuality needs women to talk about sex, intelligently, out loud and in public (not just on Mumsnet) or it will forever remain a source of shame. Moran has been a columnist since she was a teenager, and while she has always been idiosyncratic, I'm not sure that I would have described her as radical. But there is iconoclasm lurking under every one-liner. I realised I have never read an account of someone's period starting. The closest I can even think of is Sarah Silverman's memoir about wetting the bed. I have never read a woman writing about wanking while fantasising about Chevy Chase (or anyone else; Chevy isn't the radical bit, here, although I do now see him in a whole new light). I have never read a sentence like this: "There is a great deal of pleasure to be had in a proper, furry muff . . . Lying in a hammock, gently finger-combing your Wookiee whilst staring up at the sky is one of the great pleasures of adulthood." I have read some of Moran's arguments about porn (though none so comically expressed); other insights are so shiny, neat, self-evidently right that it was like she was potting a snooker ball in my brain. This one about binge eating is an example:

"Overeating is the addiction choice of carers, and that's why it's come to be regarded as the lowest-ranking of all the addictions. It's a way of fucking yourself up whilst still remaining fully functional, because you have to. Fat people aren't indulging in the 'luxury' of their addiction making them useless, chaotic or a burden. Instead, they are slowly self-destructing in a way that doesn't inconvenience anyone. And that's why it's so often a woman's addiction of choice. All the quietly eating mums. All the KitKats in office drawers. All the unhappy moments, late at night, caught only in the fridge-light."

Structurally, the argument-told-as-memoir is not easy to pull off. A life told in comic episodes will not arrange itself neatly along feminist or any other ideological lines. The exigencies of the argument mean that the chapters have a very different emotional weight, so that the one on abortion is nothing like the thumping heart of the one on menstruation. The prose is columnistic, in that it's quite informal and very conversational; the sensation of having Moran in your house can be uncanny. But essentially, she's a comedian; her cadence is comic, her punctuation is comic, her wordplay is mischievous, and all this before you even touch on her observations. The irresistible pull of self-parody gives each paragraph a gravitational urgency. "I am a virgin and I don't play sport, or move heavy objects, or go anywhere or do anything, and so my body is this vast, sleeping, pale thing. There it is, standing awkwardly in the mirror, looking like it's waiting to receive bad news. It is the bad news." She can be funny in a terse, edgy way: "In those days, the music scene was much like Auschwitz. There were no birds. You couldn't find a woman making music for love nor money." She can be funny in a more expansive, absurdist way: "The problem with the word 'vagina' is that vaginas seem to be just straight-out bad luck. Only a masochist would want one, because only awful things happen to them. Vaginas get torn. Vaginas get 'examined'. Evidence is found in them. Serial killers leave things in them, to taunt Morse . . . No one wants one of those."

Page for page, my favourite chapter is "I Am in Love!" It's purportedly a story about falling in love with an unpleasant man, but I read it as a love letter to sisterhood, with a small "s"; a love letter to her actual sister, Caz. But in terms of changing the world, the momentous thing is to talk so freely about her body and its functions, in "a culture where", she says, "nearly everything female is still seen as squeam-inducing and/or weak". Germaine Greer, in a review that was warm but a bit salty, like sperm (sorry, I am essaying a new sexual openness – it is not as easy as it looks), ends: "More disconcerting is the way that Moran revisits themes that I have written thousands of words about, and even made TV documentaries about, the C-word and pornography for two, and restates my case in pretty much the same terms, with not the faintest suspicion that anyone has ever said any such things ever before." One can see how irritating this would be from Greer's perspective, and also how much it would have ruined Moran's momentum to have to finish everything pace Germaine. But what makes this book important is something unique to Caitlin Moran; she and Greer have both attacked the elemental shame attached to being a woman, but where Greer was furious, Moran sloughs it off with exuberance. There is a courage in this book that is born, not made, and not borrowed, either. It is vital in both senses.

In her prologue, Moran bemoans the fact that the women's revolution "had somehow shrunk down into a couple of increasingly small arguments, carried out between a couple of dozen feminist academics, in books that only feminist academics would read". Sylvia Walby, Unesco chair in gender research at Lancaster University, would probably concede that her audience is small, but would trenchantly contest that her arguments are small too. Hers is a densely written book, whose propositions proceed from one to another with the unforgiving directness of a quadratic equation. If you need a bit of breathing space, you can do it in your own time. It repays the effort, though, in the following ways. First, she addresses raunch culture or, if you prefer "post-feminism", which preoccupies and, I sometimes think, mires feminists, often creating discord between the second and third wave that needn't exist. "Raunch culture," Walby writes, "is bound up with the neoliberal turn, with its commercialised and competitive approach to intimacy. The alternative social democratic form is based on mutuality and equality. Hence, a celebration of innovation and experimentation in intimacy and sexuality, in the context of mutualism and equality, is aligned with feminism, while competitive commercialised sex is not." This is the message I take from that – though Walby, enemy of the broad brush stroke, would probably correct me: do what you want, girls, so long as you do want it. So long as it's in the service of your own sexual pleasure, and not to score some competitive advantage by manipulating the pleasure of someone else.

Walby takes great care to examine what we might call the disappearance of feminism, demonstrating that its change in nature has led to a change in visibility – far from having failed, this new low profile is actually testament to its "intersectionality". Again, I am putting this crudely, but feminism started out as a protest movement, so made a lot of noise; a process of persuasion has put feminists and their aims at or near the centre of governments, in many countries, so of course the protest element has been largely replaced by constructive, fruitful political engagement, which takes place with much less fanfare. She reminds us of so much that has been achieved, and alerts us to changes in gender equality architecture at a European level that would make Richard Littlejohn's eyes pop out. She explores the ways in which feminism can work with other aims, what the crossover is between feminism and environmentalism, and what the implications are of the financial crisis. But the strongest message of this book is that neoliberalism "makes the achievement of feminist goals more difficult. The increase in economic inequality and the decrease in the legitimacy of state action alter the context in which feminism makes its demands."

Her writing style is so restrained and so disciplined, that it takes some time to realise the impact of what she is saying: first, that feminism cannot thrive against a wider backdrop of inequality, and second, that feminists have a duty to more than just women. We are a battalion in a wider fight against the trend towards inequality. I found this a heartening and timely book, a proof against demoralisation, a warning against internecine splits. I also changed my mind about various things – unions, for one (they were somewhat slow off the mark in taking women seriously as a force worth allying with; but Walby shows these alliances were, and always will be, crucial); quotas, for another. It's interesting that Moran, from a totally different direction, arrives at roughly the same place – that quotas are a good thing. She says about sexism: "I don't really see it as men vs women at all. What I see, instead, is winner vs loser. Most sexism is down to men being accustomed to us being the losers. That's what the problem is. We just have bad status." The endpoint of both these very different books is that feminism has no meaning unless it's tied to a belief in equality overall.

The editor of Granta magazine, I dare to hope, when calling the latest edition"The F-Word" is referring to "female" rather than "feminist". If not, he has fallen into that GCSE syllogism: this book is about women; women are feminists; ergo this book is about feminism. Caroline Moorehead's "A Train in Winter", which describes the arrival of 230 French female resistance fighters in Birkenau, does seem to be attempting a feminist angle on the Holocaust at one point: "Block elders [were] for the most part German criminal prisoners who effectively collaborated with the SS and whose own survival depended on brutality. Their viciousness and vindictiveness was said to surpass by far that of their male counterparts." It's an interesting story, sensitively written, but a) this sounds suspiciously like one of those Daily Mail observations –"isn't it amazing that it's often women who bully other women?" – which, frankly, is not very feminist and b) I think it's pushing it to present the Nazis or any of their works as an outrage against women. Their brutality seems to have been fairly even-handed, or if it wasn't, the men surely suffered enough not to be presented as the winners of the atrocity. Julie Otsuka's "The Children" is a wonderful, mellow, seamless tale of first-generation Japanese immigrants to America. The most overtly feminist pieces include AS Byatt's "No Grls Alod. Insept Mom" (a notice attached to her five-year-old grandson's door), a short inventory of clubs she'd encountered that wouldn't allow girls or women. And Rachel Cusk's "Aftermath", a tantalising excerpt from her divorce memoir, which comes out next year.

Cusk's characterisation of feminism starts strangely: "Then again, the feminist is supposed to hate men. She scorns the physical and emotional servitude. She calls them the enemy." This isn't a sophisticated reading of feminism, so the author is clearly ascribing this belief to someone other than herself. But to whom? To mainstream society? To the past? To her soon-to-be ex-husband? I felt foolish not knowing, but then it struck me that it didn't matter. Why start a conversation about ideas with what a mistaken person thinks? Why not start with what you think? The next paragraph brings us, it seems, closer to Cusk's territory: "I suppose a feminist wouldn't get married. She wouldn't have a joint bank account or a house in joint names. She might not have children, either . . . I shouldn't have called myself a feminist because what I said didn't match with what I was."

Again, these definitions are curious. There is an argument that marriage reinforces the patriarchy, but there is no precept in feminism against sharing your wages. If you object to money or property held in common, that's not feminism, that's possessive individualism (the two are confused with one another, but not often on this subject). And a vision of feminism that involves eschewing reproduction altogether is like a vision of environmentalism that involves ending reproduction: it might work, but it would have the iatrogenic consequence of species suicide. This is not standard feminism; nobody would try to live by it. This is separatist feminism, the sort that makes young women say "I'm not a feminist".

This was written in fresh anger; Cusk is still very much in the throes of de-marriage. Aside from the confused versions of feminism – and the contortions do seem to be down to the splenetic mood – there are elements that are really indefensible from the husband's point of view, unless his return were to be added as an appendix. Cusk writes: "My husband believed that I had treated him monstrously. This belief of his couldn't be shaken; his whole world depended on it." It leaves the strong impression that she has plenty of beliefs of her own that she doesn't want shaken, and yet she has "come to hate stories. If someone were to ask me what disaster this was that had befallen my life, I might ask if they wanted the story or the truth." He, in this version, is blinded by his need for a narrative, while she plugs directly into the truth. It's a little bit partial. At one point, she describes their family situation – her husband gave up work to look after their daughters – as the result of her unwillingness to play the maternal role. This "cult, motherhood, was not a place where I could actually live. It reflected nothing about me: its literature and practices, its values, its codes of conduct, its aesthetic were not mine." And so she "conscripted" her husband into the care of the children. Less than a minute later (in reading time), a solicitor told her she would have to continue supporting her husband, financially, when they split up. "But he's a qualified lawyer, I said. And I'm just a writer. What I meant was, he's a man. And I'm just a woman . . . the solicitor raised her slender eyebrows, gave me a bitter little smile. Well, then he knew exactly what he was doing, she said." Whether she imputes that view to the solicitor or not, Cusk still wants it both ways: we're asked to imagine her ex as such a magnificent lawyer that he managed to make her feel as though she were conscripting him, when all along, they were working to his long-game. Her feelings of maternal alienation were, in this version, a confection of his, with the aim of divorcing her some years down the line and pinching half her salary. Not since we met Heathcliff have readers been presented with an anti-hero whose grudges are so intricately prosecuted.

But she's like a lion, depositing a trophy kill: you might feel a bit queasy about it from some angles, but there is so much meat here. "Help is dangerous because it exists outside the human economy: the only payment for help is gratitude," she writes, distilling that awkwardness between couples, especially between parents, the tightrope between being put-upon and beholden. There is something marvellous, even monumental, about her honesty, the unabashed importance she attaches to every event: "I went to Paris for two days with my husband, determined while I was there to have my hair cut in a French salon. Wasn't this what women did? Well, I wanted to be womanised; I wanted someone to restore to me my lost femininity. A male hairdresser cut off all my hair, giggling as he did it, amusing himself during a boring afternoon at the salon by giving a tired blank-faced mother of two something punky and nouvelle vague. Afterwards, I wandered in the Paris streets, anxiously catching my reflection in shop windows. Had a transformation occurred, or a defacement? I wasn't sure. My husband wasn't sure either. It seemed terrible that between us we couldn't establish the truth." There is a topnote of derision for her own sex ("wasn't this what women did?") that is a much more likely wellspring than Cusk's divorce for her suspicions over whether or not she is still a feminist. But sisterliness and feminism have never been interchangeable; they are less so now than ever, as the expansion of our choices has shaped us into so many varieties.

Her final paragraph is evocative to an almost supernatural degree: "I begin to notice, looking in through those imaginary brightly lit windows, that the people inside are looking out. I see the women, these wives and mothers, looking out. They seem happy enough, contented enough, capable enough: they are well dressed, attractive, standing around with their men and their children. Yet they look around, their mouths moving. It is as though they are missing something or wondering about something. I remember it so well, what it was to be one of them. Sometimes one of these glances will pass over me and our eyes will briefly meet. And I realise she can't see me, this woman whose eyes have locked with mine. It isn't that she doesn't want to, or is trying not to. It's just that inside it's so bright and outside it's so dark, and so she can't see out, can't see anything at all."

Cusk gazes at herself unblinkingly, and judges harshly what she sees. But to call herself not a feminist? Hahaha. Of course she's one.

• This article was amended on 28 June 2011, correcting the spelling of Shere Hite