Cheating on one's partner(s) is considered a bad thing in most societies; it's definitely often taboo. With "cheating", I mean engaging with another human being in an intimate way, without your life partner's/partners' consent.
What I am currently struggling with, is how something as carnal as sex or kissing can be considered so morally wrong, when engaging with other people through friendship is universally lauded. In friendships, we share our thoughts and feelings—something much more private than one's body, I'd say.

Don't get me wrong: I personally feel very strongly (i.e. negatively) about cheating. That's the reason I'm trying to view these matters rationally—I can't keep living my life with my current views and feelings on it.

  • To clarify, are you asking (1) is cheating morally wrong? or (2) why do people consider cheating wrong? It seems that of the two current answers one addresses 1 and the other addresses 2.
    – E...
    May 6, 2016 at 19:27
  • "... it seems implicit it in the OP that what was meant was "Cheating - assuming the person doesn't care about his.her partners feelings or the partner doesn't care" - if that isn't the case, then the answer to the OP is trivial: "It is wrong because it hurts the partner's feelings"" --From Alexander's comment on his answer. Can you clarify whether this is what you meant or not?
    – Era
    May 6, 2016 at 20:49
  • @Eliran: I fail to see the difference between "morally wrong" and "what people consider wrong". May 7, 2016 at 9:44
  • 1
    There is an important difference. One question is normative (i.e. what are people ought to do), and the other is descriptive (i.e. what do people actually do). You could answer the moral question with some moral philosophy, like Alexander S King's answer, and the descriptive one with cultural or psychological stuff, somewhat like Cort Ammon's answer.
    – E...
    May 7, 2016 at 9:50
  • @Era: This is not a trivial matter at all. Even if the partner's feelings are hurt, I'm not sure this automatically makes the actions of the cheater "bad". I'd day he/she is disrespectful, but I am not sure hurting one person's feelings over another's (or possibly multiple others'), is necessarily bad. "The others", of course, being the cheater and any possible side-partners. May 7, 2016 at 9:52

7 Answers 7


Several perspectives can be offered (as a complement to Cort Ammon's answer):

Kantian perspective

It is possible to examine the question from the perspective of Kant's categorical imperative:

"Act only according to that maxim whereby you can, at the same time, will that it should become a universal law." - Kant, Immanuel (1993) [1785]. Grounding for the Metaphysics of Morals. Translated by Ellington, James W..

So what happens if cheating becomes universal - that is if everyone starts sleeping with whomever they wanted to, regardless of relationship status? The concept of romantic relationship would loose its meaning altogether. One could then argue that given how much of our society is built around courtship and relationship status, this would be an overall bad thing.

Consequentialist/Utilitarian perspective

John Stuart Mill says in "Utilitarianism":

It is quite compatible with the principle of utility to recognise the fact, that some kinds of pleasure are more desirable and more valuable than others. It would be absurd that while, in estimating all other things, quality is considered as well as quantity, the estimation of pleasures should be supposed to depend on quantity alone.

Per this principle, sexual pleasure/connection, although desirable, is not as valuable as friendship at the level of ideas and emotional connection. Then, based on utility, one could argue that sexual relations might interfere with real friendships, and so friendship should be prioritized over sex whenever the two compete.

Evolutionary perspective

One could argue that there is nothing morally wrong about "cheating" but that fidelity makes sense as an evolutionary strategy. According to Strategic Pluralism Theory for example, it makes sense in many environments for people to restrict themselves to one partner and focus on maximizing the care provided to the offspring of that relationship. In other environments, other strategies might used. See Gangestad, S. W.; Simpson, J. A. (2000). "The evolution of human mating: Trade-offs and strategic pluralism". Behavioral and Brain Sciences 23: 573–587.

Religious/Social perspective

I can't provide a source for this. It was an answer provided by my high school religious studies teacher. The Abrahamic religions had very strong rules against promiscuity because of the need to preserve family lineage. In societies were family and clan relationships were very important, people had to be sure that siblings and cousins were indeed who they claimed they are. At a time when contraception or DNA testing weren't available, the only way to insure the "purity" of family ties was by restricting the sexual partners that people could have.

  • The immediate utilitarian reaction, for me, is simply that you would hurt your partner's feelings if you cheated. (So that the hurt feelings outweigh the pleasure.) Also, under Utilitarianism you seem to talk about sexual relations in general and not about cheating.
    – E...
    May 6, 2016 at 19:15
  • @EliranH a) A strict utilitarian would be thinking only of her/his own pleasure and would presumably not care what the partner feels, only what the consequences of the partners feelings are. I am presuming the principle of utility from a private perspective (per my interpretation of the OP). b) I say "so friendship should be prioritized over sex whenever the two compete." presumably one or to of the parties being in another relationship counts as friendship and sex competing. May 6, 2016 at 19:44
  • I've never heard that definition of "strict utilitarianism" before. It sounds like ethical egoism to me; what's the difference?
    – Era
    May 6, 2016 at 20:13
  • @Era I used the term, I did not intend it as a term of art. And I realize I was mistaken in using it. That being said, it seems implicit it in the OP that what was meant was "Cheating - assuming the person doesn't care about his.her partners feelings or the partner doesn't care" - if that isn't the case, then the answer to the OP is trivial: "It is wrong because it hurts the partner's feelings" - as you said in your first comment. That is why I framed the utilitarian response the way I did. May 6, 2016 at 20:38
  • @Alexander: Thank you, for your wonderfully detailed answer. I don't mean to gloss over the Kantian perspective, but I will say that I'm not sure a complete overhaul of modern society would be bad. Change is scary. I know. ;) I take great comfort in what you said after that John Stuart Mill quote, and have accepted your answer for it. "Friendship should be prioritized over sex whenever the two compete." A fantastic insight. May 7, 2016 at 10:06

Consider the game of "blackjack." Your goal is to get as close to 21 as you can, but not go over.

Morals and taboos like these are very cultural. They shift from culture to culture. In fact, they can even shift from sub-culture to sub-culture (see: swingers). The takeaway may be that some cultures see some facets of society as similar to the blackjack game. The goal for a facet defined as such would be to get as much as you can, but not to go so far as to go past a line. If the culture chooses to express such goals in its handling of relationships, it is reasonable to assume "cheating" will get defined as such.

One thing to consider is the power of the "nuclear family." In cultures which have the nuclear family, the relationship between husband and wife is typically given an elevated level of importance. The line between "being friendly" and "cheating" may exist because it was found to be a biologically meaningful line in the sand between behaviors that could be shared by all and behaviors which "should" be reserved for husband and wife.

You also see this in many culture's dealings with death. There are a lot of things that are acceptable, but because death is so permanent, it is often given a special standing. It often becomes a line that one "should" not cross.


It might seem like promiscuity is victimless, but in fact, in the larger overall social picture, promiscuous sexual contact is a) a significant disease vector (there are many serious diseases which spread primarily or exclusively through sexual contact) and b) likely to result in poor parenting outcomes for several reasons (unwanted children, children with undesirable partners, weakening of the social bond between fathers and their children), at least in the case of heterosexual promiscuity. For those two reasons, there are strong prohibitions against promiscuity in most traditional moral frameworks.

In the modern era there are reasonably reliable methods of preventing or reducing both sexually transmitted disease and unwanted pregnancies. This lessens the social harm of promiscuity --at least in the case where the methods are used consistently and effectively. However, this doesn't mean that it's possible for everyone to immediately readjust, either socioculturally or biologically. Not everyone is well-suited to experiencing the emotional intimacy of sexual contact with large numbers of partners.


Basically, it's just cultural prejudice.

Bonobos share 98.7% of their genome with both humans and chimpanzees, yet bobonos do not share this same prejudice. In bonobo society, sexual activities with friends of either gender are not only totally normal but often fulfill the same role as a handshake or small-talk in human interaction.

As Jack Hitt writes for Lapham’s Quarterly:

Bonobo society is based on cooperation and empathy; the culture is a matriarchy where competition is redirected into a communitarian sexual appetite. Bonobos also shocked these earliest scientists because they possessed a cheerful sense of general promiscuity, weaving wanton sex into their society, and they boasted a sexual repertoire once thought to be the exclusive property of Homo sapiens — deep kissing, foreplay, oral sex, homosexuality, and polyamory.

There is more :

Throughout the day, males and females, adolescents and elders alike greet one another sexually for apparently almost any reason — and do so with everything from a quick feel, to porn-style choreographies, to elaborately athletic couplings. This feature — the variety of their easygoing sex life — is what led Duke primatologist Vanessa Woods to cheekily title her book about them Bonobo Handshake. Bonobos have deployed their elaborate sexual toolkit to ease all kinds of social transitions — ranging from saying good morning to giving the blessing before dinner to expressing a hearty welcome to a new member of the group. Females will casually present themselves to males. The male will walk right up to a female without any hesitation. All bonobos frequently have homosexual sex — the males being quite fond of hanging upside down, face to face, from a tree and engaging in what the gay community calls frottage (some primatologists call it “penis fencing”; to most teenagers it’s better known as dry humping).

There’s way more and you can/should read it here.

According to Dr. Christopher Ryan, there are seven things we can learn about love from bonobos:

  1. More sex = less conflict. As the great primatologist, Frans de Waal put it, "Chimps use violence to get sex, while bonobos use sex to avoid violence." While chimps victimize each other in many ways—rape, murder, infanticide, warfare between groups—there's never been a single observed case of any of these forms of aggression among bonobos, who are much sexier than chimps. As James Prescott demonstrated in a meta-analysis of all available anthropological data, the connection between less restrictive sexuality and less conflict generally holds true for human societies as well.

  2. Feminism can be very sexy. When females are in charge, everyone lives better (including the males). While male chimps run the show, among bonobos, it's the females who are in charge, with much better quality of life for everyone involved (see #1).

  3. Sisterhood is powerful. Although female bonobos are about 20% smaller than males—roughly the same ratio as in chimps and humans—they dominate males by sticking together. If a male gets out of line and harasses a female, ALL the other females will gang up on him. This sisterly solidarity, combined with lots of sex, tends to keep the males behaving politely.

  4. Jealousy isn't romantic. While bonobos no-doubt experience unique feelings for one another, they don't seem to worry much about controlling one another's sex lives. Nor do bonobos seem to gossip much...

  5. There's promise in promiscuity. All the casual sex among bonobos is arguably a big part of what has made them among the smartest of all primates. Until human beings came along and messed things up for them, bonobos enjoyed very high quality of life, low stress, and plenty of social interaction in hammocks. In fact, of the many species of social primates living in multi-male social groups, not a single species is sexually monogamous. Each of the arguably smartest mammals--humans, chimps, bonobos, and dolphins—is promiscuous.

  6. Good sex needn't always include an orgasm, and "casual" doesn't necessarily mean "empty" or "cheap." Most bonobo sexual interactions are nothing more than a quick feel, rub, or intromission—a "bonobo handshake," if you will. (See Vanessa Woods's excellent book by that name for a personal story of living with bonobos while falling in love.) But bonobos are very romantic: like humans, they kiss, hold hands (and feet!), and gaze into one another's eyes while having sex.

  7. Sex and food go together better than love and marriage—at least for bonobos. Nothing gets a bonobo orgy started faster than a feast. Give a group of bonobos a bunch of food and they'll all have some quick sex before very politely sharing the food. No need to fight over scraps like a bunch of uncouth chimps!

While I can't say I take Ryan's conclusions for granted, I definitely agree that we - as a species - could learn a lot about ourselves and why we do the things we do by comparing ourselves with chimps and bonobos... two species with respectively a patriarchic and a matriarchic societal structure, and cultures that in some areas couldn't be more different from one another... in spite of 98.7% shared DNA!

  • In the book "Why is sex fun?", Jared Diamond compares humans, bonobos, and a lot of bird species that have varying degrees of couple relationships, partner exclusivity and faithfulness. I strongly recommend this book.
    – Stef
    Dec 26, 2022 at 19:14

Some things just need to be grounded in biological fact and consequences.

Friendships do not produce children, and we want to have one model of sexuality for both straight and gay relationships.

Ambiguous parentage leads to strife over which potential parent (or parental clan) gets legal control of the child's living conditions, which can easily scar the child, especially if it happens before the 'age of reason' where the child can logically absorb the two parent's agendas and play along.

In previous social arrangements tied even more directly to biology, for instance, Attic Greece, that has meant that one could have it both ways, but only if one split the sexes the right way. Since gay relationships don't produce children to fight over, only property, one could have (as did Sappho) a spouse, and a number of lovers of your own sex.

But our modern taste for consistency and equality means that this double standard offends us, and we want everyone to be monogamous for extended periods.


In a wealthy modern technological society, this may no longer be so relevant, as we have genetic means to ascertain fatherhood, and we have strengthened our social conventions for both separated parents and effective adoption when the parents choose to be separated from their responsibility. We are almost to the point where the resources consistently exist to make those inefficient systems work to an acceptable degree. So, given a tiny bit more tolerance for complexity, and a little more money, we might slowly reduce this bias.

(Of course, as a gay man, I see this deduction as a bias because it is a consequence of the presumption that the straight model is the right one, and that sex is primarily about children.)

But our moral code is fixed much earlier in time.


Let us take the game of football. People kick balls and try to put the ball into the goal. What happens if one person touches the ball and gets away with it ? What happens if one person could atomize the ball , hide it in his shirt and reatomise it back in the goal without anyone noticing ? You could , nothing right or wrong about it. But the reality is,without the rules of football being football,it is not football anymore. And any player who loves football would want to play the game as it is. Ensure its continuity lest it becomes atomizerball.

Why do people get into relationships ?

To fulfill certain emotional, physical and various other kinds of needs. A relationship is a relationship only when certain rules are followed. Else it is not a relationship. You could sleep with the whole world while you are at it , you could remain a virgin. I think it is not a question of morality, but of reality. The reality is the person who cheats has no love for the sanctity of the rules of the relationship. If so, better to play atomizer ball to your hearts content.

  • I'm not sure the rules need to be transparent. I think relationships can exist with hidden rules, rules that can and will be broken, if both parties can live with this situation. The issue is not so much about the people involved in the relationships themselves, but about societies' views upon it, and how their views influence those people. Without the rules of societies, people in a relationship only need to agree among each other. May 7, 2016 at 9:42
  • society consists of individuals. Which is why I said mot a question of morality. Morality is collective ideology dependent on society. Reality is not dependent on any entity , but encompasses it.
    – Sid
    May 8, 2016 at 20:06

I would say for strictly cultural reasons. You could come up with all sorts of almost game theoretic explanations for it, but I feel those are naive: it is not hard or outlandish to imagine a society who treats the subject differently. For instance, I believe in Islamism and even in some Christian communities, men have many wives: this would fit in your definition of "cheating". So, it is probably just the way that our Western society is allegedly organised.

Having said that, it is not hard to find people even in modern Western cities who don't conform to this at all, in fact, I would call it somewhat common - that's why I said " allegedly organised". That and, personally, I find that most people don't really have deep friendships at all, and for them such conjugal relationships are the deepest/most intimate they get - hence not holding friendships in such high regard.

  • How would having multiple wives fit the OPs definition of cheating (which requires not informing or having the consent of the other sexual partner)? My sense is that in groups that practice it, the wives are not unaware or not consenting (perhaps indirectly) to a system where they are not the exclusive wife.
    – virmaior
    May 26, 2016 at 13:17
  • "Unaware or not consenting": first, I don't think in the situation I described the husband needs the previous wives' consent in order to marry another one. Then, I think OP felt the need to explicitly say "unaware" precisely because extramarital relationships are, due to cultural standards, immoral, hence the need for explicit consent of the partner. You don't need consent of your partner to have friends (YMMV) - I used that as a situation where having extramarital relationships is not something for which you have to ask.
    – wet
    May 26, 2016 at 14:07
  • Lastly, it's fine if you don't agree that this example reflects a situation where extraconjugal relationships are culturally OK: the previous phrase, "it is not hard or outlandish to imagine a society who treats the subject differently", still stands.
    – wet
    May 26, 2016 at 14:09
  • "You don't need consent of your partner to have friends" I very strongly disagree. If my partner didn't consent with me having friends, then I would likely leave my partner immediately. I wouldn't "stay with my partner and have friends without my partner's consent".
    – Stef
    Dec 26, 2022 at 19:11

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