Since the age of thirteen or so, my female cohorts and I have defined womanhood through a handy set of quantifiable—or tangible, at least—measures: bra size, dark eyeliner, use of tampons, relative intactness of one’s hymen, smoking, being “eaten out.” From there, the relevant metrics have only accumulated: a double-digit number of sexual partners, being able to fuck like a man, a long-term boyfriend, securing a respectable profession, refusing to go dutch on dates, being able to fuck like a lady, paying rent, and so on. But now, at the precipice of thirty, I’ve found that the single experience that divides women from girls is loss. The Big Reshuffle, The Divorce, or, as some of my friends and I call it, simply The Event. The first true loss of intimacy, security, and love in a woman’s life typically brings her face to face with the terror of being alone: She must endure the insane pounding of her own heart and not go mad. This is what Erica Jong’s classic novel Fear of Flying (fortieth-anniversary edition, Henry Holt, $35) is really about: being snipped from the emotional strings that tie you to a man, going into free fall, and, perhaps, learning to fly.

Jong puts the test to Isadora Zelda White Stollerman Wing, a Jewish-princess poet who accompanies her silent, stewing psychoanalyst husband to a shrink convention in Austria. At the congress of analysts, Isadora becomes infatuated with Adrian Goodlove, an impoverished, swinging existentialist therapist. Adrian, with a leering London accent, playfully calls Isadora a “cunt,” compliments her “fat ass,” and convinces her to join him on a trek across Europe with no plans and no promises.

Isadora wrestles with her own existentialist dilemma courtesy of her affair with Adrian: Should she flee her husband for good, or return to the security, and perhaps the stultifying insularity, of her marriage in New York? Jong uses Isadora’s crisis to examine all the ways women resist this moment that sends them either falling or “flying”—through marriages, through romance, through sex, through settling, through compromising, through infidelity, through limp-dick blow jobs given to men with European accents. And her language and insight into the war between freedom and intimacy mark the true genius of her novel forty years on. “If we haven’t the power to complete ourselves,” Isadora muses after Adrian abandons her in Paris, “the search for love becomes a search for self-annihilation; and then we try to convince ourselves that self-annihilation is love.”

Jong’s smutty language—“warhead pricks,” “finger-fucking to Frank Sinatra,” “silky” penises that taste “faintly of urine”—and her brazen depiction of female desire (Isadora has the “restlessness, the hunger, the thump in the gut, the thump in the cunt, the longing to be filled up, to be fucked through every hole, the yearning for dry champagne and wet kisses”) prompted many critics to compare her landmark novel to an equally graphic celebration of male desire: Henry Miller’s Tropic of Cancer. Indeed, the two are now routinely cited as among the best exemplars of “racy” literature in the American canon. But neither novel is really about sex. Tropic of Cancer has far more passages about hunger than it does about mad carnal encounters. And Fear of Flying has much more to do with loneliness than with fucking or feminism.

Feminism is, indeed, a pretty strange bedfellow for Isadora’s exploits. Now that it’s officially middle-aged, with a fortieth birthday to celebrate, Fear of Flying might be regarded as one of the hallowed texts of second-wave feminist thought, but its true value is in the way it reclaimed many nonpolitical features of sexuality during an intensely politicized phase of America’s intimate life, by eliciting core questions of transgression, self-identity, and loss. And now that we are well into a depoliticized era of feminist thought, Jong’s particular brand of solipsistic feminism, which treats aesthetic and political values as interchangeable, has proved the least interesting and most dated feature of the novel.

Now, I readily concede that I am very much disposed to float this critique because I was raised by a woman—my mother, a Chilean immigrant from 1950s Latin America—who has begged me to read this book ever since I sprouted breasts in the 1990s. But I ignored her yellowing paperback, as I was uninterested in the sexual struggle of women who were butting against the moral code of Calvinism and the concept of the “immature orgasm.” That was not my fight. I grew up with a kingdom of broadband pornography and took my first Plan B pill at fifteen; I had bigger issues on my hands. In many ways, I was born liberated.

Nevertheless, it’s crucial to zero in on the novel’s skewed ideological constructs, since Jong’s uncritical embrace of a self-centered political aesthetic now also encapsulates the central failings in feminist thought today. (Besides, it would be an ironic concession indeed for me to downplay my reservations about the identitarian outlook of a feminist novel so deeply engaged with the sexual politics of self-exploration by making my criticisms here all about me.)

The “big problem,” as Isadora proclaims, is “how to make your feminism jibe with your unappeasable hunger for male bodies. It wasn’t easy.” But this is not a feminist problem. The motivations behind sex are apolitical; they are derived from passion, good conversation, mania, loneliness, alienation, or booze. A feminist problem is the wage gap, limited access to abortion, harassment in the workplace, but none of these things determines just who you want to fuck and why. You can employ some sort of feminist aesthetic critique to get at why women want to fuck certain men—are we attracted to alpha males who reinforce society’s codes of female inferiority? would more men want to fuck us if we acted like Taylor Swift? is Taylor Swift a feminist even if she says she’s not?—but what a waste of energy.

This same tiresome scramble of aesthetic values and feminist thought mucks up the introduction to this new edition of the novel. The chick-lit impresario Jennifer Weiner (Good in Bed, In Her Shoes) frames Fear of Flying as the ultimate redemption of her own popular genre. She writes a piddling polemic about the “double standards” that govern the way female and male authors are treated for rendering sex on the printed page. “The books men write simply matter more. They are more frequently reviewed, their authors are more frequently profiled.” To clinch this case, Weiner quotes Jong’s observation that women writers are “confined to the ghetto of popular culture.” Weiner’s greatest praise, then, is that Isadora, who grew up wealthy in a gold-leafed Central Park apartment, discovers the inner courage to be—yes—a writer! This is a painfully insipid but ultimately telling representation of current feminist self-obsessions.

Much the same myopia of privilege and puerile rebellion afflicts the character of Isadora and her epic quest for the “zipless fuck,” the now duly canonized term for no-strings-attached sex—a notion that also belongs to another era, when sexual liberation had not yet uncoupled itself from aesthetics. “The zipless fuck is absolutely pure. It is free of ulterior motive. There is no power game. The man is not ‘taking’ and the woman is not ‘giving.’ No one is attempting to cuckold a husband or humiliate a wife. No one is trying to prove anything or get anything out of anyone.” But after this idealized litany of its effortless virtues, Isadora concedes that a zipless fuck “is rarer than a unicorn.”

No shit. That’s mainly because the idea that nobody has anything to prove in a zipless fuck simply isn’t true. Indeed,the female partner is trying to prove a very specific point: that she can fuck just like a man, without the specters of rape, murder, pregnancy, or abortion lurking somewhere in her brain. The quite ideological point of the encounter is, in other words, to unburden herself from all the hang-ups that are so specific to the female experience in the sexual arena. Meanwhile (and far more predictably), the male partner is trying to showcase his own sexual prowess; otherwise, why bother? Sex with strangers, sex without intimacy, once the first rush of new smells and hands wears off, is not an uplifting experience. It usually leaves a residue of shame and horror—that’s partly what makes it so thrilling at the time.

So for today’s readers of Jong’s novel, Isadora’s “problem” might well be restated as something like this: Why should a woman go through such emotional acrobatics to prove such a minimal and depressing point? That she can fuck like a man? That her orgasm, if she has one, is free from emotional attachment? Great! Now, darling, tell us how your orgasm will close the wage gap between men and women. The orgasmic economy of the ’70s is null in 2013. Jong recognizes that there’s a war between men and women, but she chooses the wrong weapon in the struggle.

After Adrian abandons Isadora in Paris (so he can head to Cherbourg to visit his girlfriend and kids), Isadora is thrust into an opportunity to have a zipless fuck in a train compartment with a stranger who grabs at her crotch. She is repulsed. “Puzzling, wasn’t it? A tribute to the mysteriousness of the psyche. Or maybe my psyche had begun to change in a way I hadn’t anticipated.” The markers of maturity must evolve.

For all of its class-bound preoccupations and the cramped horizons of its political vision, Fear of Flying does remain an important document, of both the literature and the emerging gender protest of its age. Its greatest triumph is the depiction of a female psyche battling the forces of loneliness while still yearning for pleasure. It’s a brilliant portrayal of how differently women experience existentialism, romance, and solitude. This is a distinction that’s been washed out of the umpteen waves of feminism: Men and women are different. Women experience the world differently, through their bodies and minds alike. The challenge going forward, though, is to wrest a working feminism from this insight that spurs women to define their similarities, and advance their common interests, without any obsessive reference to men, or the zipless fucks they may or may not choose to dispense.

Natasha Vargas-Cooper is a freelance journalist based in the San Fernando Valley, California.