The invitation arrives on thick ivory stock. Friday night, city skyline, a private dining loft where “conversation will be our principal course.” The host is the sort of man who can conjure a guest list from four continents and still arrange the seating so an evolutionary biologist faces a Benedictine monk. You accept out of curiosity, perhaps vanity, and find yourself opposite a tall woman in a silk jumpsuit, her wrists ringed with bangles that sound like late-night wind chimes. When the appetisers land, she leans in and asks—voice low, eyes bright—“Do you ever wonder whether monogamy is just a superstition we haven’t dared to outgrow?”
The table falls into that polite hush good parties cultivate. It is the oldest trick in the intellectual playbook: float a forbidden idea, then watch civilised people decide whether to pounce or pretend indifference. Someone laughs; another clears his throat. The monk smiles in a way that could be blessing or reprimand. You swirl your glass and wonder if the evening will end with a battle or a confession.
What you do not expect—what no one at the table expects—is that the woman begins to lay out, calmly and with the lucidity of a barrister, a philosophical guide to cheating. It is not, she insists, a prank or a publicity stunt. It is a thought experiment. Assume a person wants to maintain a committed partnership—mortgage, kids, Costco card—and simultaneously seek erotic novelty outside that bond. How might they build an intellectual architecture stout enough to carry the weight of their desire and their conscience, preferably without the usual load-bearing beam of deceit?
Thus the evening’s menu shifts from scallops and Burgundy to Bentham and Nietzsche. By the time espresso arrives, you realise you have heard several possible justifications for adultery, each anchored in an ethical theory respectable enough to teach at a university. You also notice that, for all the talk of freedom, nobody at this table appears entirely free. The air is delicious with risk; it is also just a little stale with self-protection.
What follows is, in spirit, her argument—expanded, detoured, cross-examined. Call it a field guide for anyone curious about how reason might conspire with appetite, and what hidden tariffs the soul pays when it travels on forged documents.
Imagine you are a utilitarian. Your moral abacus tallies consequences, not commandments. Bentham’s calculus asks only one thing: will the act maximise pleasure and minimise pain for everyone touched by it? You survey your marriage—kind, stable, but drowsy. You survey the horizon—one colleague’s teasing emails, a former lover who still pronounces your name like a secret. If you conduct an affair discreetly, spare your spouse anxiety, and return home buoyed by fresh delight, have you not increased overall utility? The vows were meant to secure happiness; if the vows now inhibit it, is not a surgical violation preferable to a messy divorce?
Utilitarianism feels exquisitely modern—data-driven, results-oriented—until you step on the first moral land mine: prediction. Ecstasy today, collateral tomorrow. Affair partners grow needs, phones mis-buzz, children catch echoes. Utility becomes a roulette wheel because people are not numbers but live wires sparking in the dark. And so the utilitarian must either possess god-tier foresight or accept a gambler’s budget for catastrophe.
Slide next to existentialism. Here the hero of authenticity storms the committee meeting of inherited norms and shouts, “I did not vote for these rules!” Sartre teaches that freedom precedes essence; de Beauvoir that love is a negotiation among autonomous projects. When an existentialist cheats, it is framed not as betrayal but as an assertion of lived truth. To sacrifice personal desire on the altar of convention is self-abandonment. Better an honest transgression than a life of “bad faith,” that terminal Parisian insult.
Yet authenticity is a stern master. Strip away contrived guilt and one is left with a subtler dread: responsibility. The existentialist cannot hide behind biology, fate, or culture; each choice sculpts the self. If your affair sets your partner ablaze with humiliation, existentialism will not permit the shrug of “accident”; the flames are authored by your hand. The moral anguish you spared yourself returns multiplied, but now it is called ownership.
Nietzsche, predictably, offers steroids for the same muscle. Man is will to power; morality is “a herd instinct in the individual.” Resentment, that slow poison of the mediocre, invents monogamy to shackle the vibrant. Cheating becomes a song of the strong. But Nietzsche’s Übermensch must also stand beyond conventional pity. Explaining to your sobbing spouse that her suffering is a bourgeois attachment to slave-morality may win points for fidelity—to Nietzsche—but forfeits any claim to human tenderness. Power tastes magnificent only if you can swallow solitude as the chaser.
Let us swivel to anthropology, where context is king. In the Ethnographic Atlas, roughly eighty per cent of recorded societies permit some form of polygyny. In these cultures, a man with multiple wives is a provider, not a villain; a woman who discreetly supplements her genetic portfolio is a strategist, not a Jezebel. Under moral relativism, “cheating” is simply disobeying your own tribe’s script. Change scripts, sin evaporates.
Yet relativism carries a hidden suitcase labeled Which culture? Your childhood bedroom? Your present postcode? That online forum where everyone swaps partners like Pokémon? Cultures overlap; allegiances blur. One might adopt Trobriand Island courting norms Monday at the hotel bar, then expect suburban Indiana loyalty by Wednesday’s soccer practice. The relativist thus risks becoming a moral migratory bird, always flying to the season that flatters desire.
Critics of monogamy sometimes reach for biology, citing evolutionary incentives: men disperse seed, women secure resources, both occasionally upgrade genes. If fidelity were natural, the argument runs, Tinder would have gone bankrupt. But basing an ethical choice on ancestral survival pressures is like building a modern salary package around the virtues of saber-tooth hunting. Naturalistic fallacy is an impatient suitor: persuasive at first glance, shabby in the morning light.
So far each philosophy dangles a permission slip, then smuggles in new demands—clairvoyance, stoic accountability, or the constant recalibration of social maps. No one gets a free lunch; the cheque is merely deferred.
Now pivot. Suppose adultery is not a private stunt but a collaborative art project. Enter consensual non-monogamy: open marriages, polycules, relationship anarchy. Here the aim is transparency, negotiated boundaries, ethical condoms. Studies conducted by Justin Lehmiller and colleagues suggest that, when honestly managed, CNM couples report relationship satisfaction on par with their monogamous peers, sometimes higher in communication scores. Jealousy exists but is treated like salt: inevitable, useful in small doses, dangerous if ignored.
It is tempting to announce case closed—philosophy is obsolete; what matters is dialogue and Google Calendar. Yet even CNM demands a worldview. Autonomy must be prized above exclusivity; love conceived as abundance, not scarcity; time portioned like venture capital among multiple start-ups. Many people test-drive the model, enjoy the thrill of emotional socialism, then discover that their heart is wired more like a monarchy: one throne, many courtiers, perhaps, but only one sovereign. Others thrive, but they put in labour hours comparable to running a boutique hotel.
Which returns us to secrecy. The point of the dinner-party thought experiment was never to promote ethical non-monogamy—it was to imagine cheating as we usually encounter it: covert, unilateral. What philosophy can pardon that? Consequentialism gambles; existentialism broods; Nietzsche roars; relativism shifts nationalities; biology pleads historical necessity. Each rationale lets the cheater slip out of shame’s handcuffs—only to discover a different shackle around the ankle.
Consider moral residue. Bernard Williams argues that even when an unethical act is fully justified—killing one hostage to save five—emotion remembers the breach. “Remorse,” he writes, “is neither the sign of moral error nor its proof. It is what a decent consciousness feels after making certain choices.” Apply that to adultery: you may prove, diagram, or tweet-thread your innocence; the residue may still cling to you like charcoal under the fingernails.
Or take moral luck, Thomas Nagel’s impish reminder that outcome matters. If a drunk driver gets home safely, society still calls him reckless; luck merely delayed the verdict. In affairs, secrecy is luck’s twin. The day text logs emerge in a divorce deposition, the utilitarian’s spreadsheet combusts. The existentialist who preached ownership now confronts a partner’s raw despair, and finds that freedom purchased by another’s unfreedom feels less triumphant.
Philosophy can armour the mind, but the body is an anarchist: eye twitch when lying, cortisol spikes, the unplanned flinch when your spouse picks up your phone. Poets call it the divided self; neuroscientists, prediction-error stress. Either way it is a slow tax on vitality. Over months, the cheater may notice that meals taste faintly metallic, or that a lover’s compliment lands with half the voltage it once carried. To compensate, they seek ever more novelty, like a climber adding oxygen as altitude thins the air.
Last comes the reckoning no syllabus can dodge: trust. Not your partner’s trust—that is obvious—but your own trust in your perceptual field. If you have grown skilled at partitioning realities, how sure are you that the partition wall will not suddenly appear somewhere else, between you and your children, your friends, your stated goals? Søren Kierkegaard warns that the self is a relation that relates itself to itself. Cheating, then, is not just duping the other; it is training the mirror to misreport.
Picture the close of that dinner party. Guests drift off, taxis streak the avenue. The woman in the silk jumpsuit lingers, gazing at the city’s constellations of rented light. Her phone buzzes—a name coded under a benign emoji—and she smiles, catlike, thumb hovering. But her shoulders sag imperceptibly, the way a scaffold does when the last builder climbs down. For a moment she looks neither liberated nor damned, only tired. You realise the night’s lecture was not a dare but a confession disguised as pedagogy: a mind cataloguing the shelters it has built against an old, persistent storm.
The elevator arrives. She offers a courteous nod and vanishes behind mirrored doors. Your reflection stares back, mildly distorted. You think about utilitarian ledgers, existential fists, polyamorous spreadsheets, and Nietzsche’s hammer. You think about residue. And you wonder—not whether cheating is philosophically defensible—but what kind of life requires so many arguments to stay upright, and how much quieter the heart might sound if it no longer had to rehearse them.
