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    Sexual Ethics

    Only when you [have sex] […] are you most cleanly alive and most cleanly yourself. […] Sex isn’t just friction and shallow fun. Sex is also the revenge on death. Don’t forget death. Don’t ever forget it. Yes, sex too is limited in its power. […] But tell me, what power is greater?1

    There is no morality intrinsic to sex, although general moral rules apply to the treatment of others in sex acts as they apply to all human relationships.2

    1. Philosophy of Sex Introduction

    While we write this chapter, a court in the United Arab Emirates have detained a foreign couple in their twenties for having sex outside marriage and if found guilty they will both face a lengthy jail sentence.3 Shortly after the 2017 General Synod vote in the UK on whether same sex couples could be “blessed” in church, the eminent theologian and academic Professor John Milbank tweeted: “There is no need to demand “celibacy” in gay relationships. That wrongly equates same sex physical affection with full (heterosexual) sex”.4 Now there might have been a subtle and sophisticated theological point here. Or there might not. Whatever the right response to Milbank is, what it makes clear, and what probably does not need pointing out, is that “sex” is, has been, and always will be an issue of great importance to people. Moreover, it makes clear that the very notion of “sex” is a philosophically interesting one. What, after all, is “sex”? What does it mean to talk about heterosexual sex as “full” sex in such a context? Was Monica Lewinsky correct to say that she did not have sex with Bill Clinton, the then president of the US, because it was “only” oral sex? What is the role of sexual pleasure in defining sex? What is consent? Is pornography wrong? What is sexual perversion? Of course, we can only deal here with a very small fraction of some of these issues (for an excellent survey of articles see Sobel 2008) and our focus will be on some of the ethical issues to do with sex.
        We start this chapter by discussing the very definition of “sex”; we then move onto discussing some of the things that different moral philosophers might say about sex. Hopefully you can see why this is the right order. For, we suggest, a lot of the ethical discussions about sex already presuppose what sex is, but that presupposition is controversial. Thus we need to be clear about the different ways to understand sex and this will enable us to explore more usefully the various moral issues associated with sex.

    2. What Is It to “Have Sex”?

    This question is not the same as what is “sexual orientation”, or, what is one’s sex — as opposed to one’s gender. There might be some that would be bemused when faced with the question “what is it to have sex?” Typical (frustrated) philosophers! Is the answer not obvious? Sex is penis-in-vagina penetrative intercourse (coitus) — end of story. Well maybe…but consider some other questions. How essential is orgasm in the definition of sex? Imagine that two people engage in coitus but there is no orgasm: is this “having sex”? What about if one person has an orgasm where the other does not? Or imagine that people are involved in manual genital stimulation to orgasm, is this sex? What about people engaged in oral sex, can this count as “having sex”? What about rape? If someone is raped is it correct to say they have “had sex”? And things get even more confusing….
        Given the definition of sex as coitus, then this obviously means that by definition homosexual sex is conceptually impossible. This might seem false and simply offensive. Sex as coitus also gives rise to some odd situations. Imagine a women asked her partner if he was a virgin and got the following response: “yes I am…I’ve only been involved in homosexual penis-in-anus penetrative intercourse”. The women might be perplexed (to say the least). She might sensibly think he is deluded in calling himself a “virgin”. Anal sex is sex, and consequently our initial definition of “sex” as coitus is incomplete.
        Notice that things are also complicated by the fact that people who are involved in sexual activity sometimes themselves report uncertainty about whether they have actually had sex. We can imagine someone being asked: “did you have sex with her?” and receiving the answer: “well it depends…” It seems then that “having sex” is a more complex notion that we might have first thought. These points are worth keeping in mind when we talk about the ethical questions that are involved in “having sex”. In particular, the reader should ask themselves if a particular account of “having sex” is being used and importantly what if that definition were changed.

    3. Natural Law and Sex

    If you recall when we discussed Natural Law Theory (NLT) in Chapter 4, something is good if that thing fulfils its function. A good knife is one that cuts well, a good guitar is one that plays well, etc. Therefore, in order to work out what “good” sex is we need to ask what sex is for. What is its function? In answering this question, we should then be able to work out what is morally acceptable sexual activity.
        St. Aquinas and other Natural Law theorists would say that our sexual faculties have one true end — procreation. True, sex is pleasurable but it is pleasurable in order to fulfil this end. If this is correct then sexual activity is good if, and only if, it is consistent with procreation and bad in so far as it frustrates that end. It is important to understand that the outcome is independent of desires, wants, reasons, hopes, fears etc. and that for the Natural Law Theorist (NLT) it is simply an objective fact whether a sexual act is wrong or right, something which is not affected by culture, religion, etc. This means that for the NLT there are objective moral truths regarding how we ought, and ought not, to behave sexually.
        We can say then that, for the traditional NLT, premarital sex, masturbation, bestiality, contraception, homosexual acts, pornography and adultery are all wrong. Premarital sex is wrong because children would be brought into the world outside the safe confines of marriage. Homosexual acts have no tendency towards procreation at all; contraception frustrates procreative ends; masturbation and pornography focus the sexual acts inwards towards oneself, frustrating procreative ends. However, it is vital to make a number of clarifications as people often misunderstand NLT.
        The NLT is not claiming that anything that frustrates natural ends is wrong but rather only human acts. So, according to the NLT, the fact that, for instance, the Bonobo monkeys engage in “rape”, “masturbation” and “homosexual” acts does not mean that they are doing something morally wrong.
        Furthermore there is a difference between using something wrongly and not using it at all. We use a knife wrongly if we try to use it as a violin bow but not by leaving it in the knife drawer. So, not using sexual faculties (celibacy) is morally acceptable for the NLT.
        However, on the face of it NLT does seem to have a lot of counter examples; there are lots of things that we agree are not wrong but do seem to frustrate natural ends. For example, imagine I regularly walk on my hands, or I am fed through a tube rather than using my perfectly good mouth, both these seem to be frustrating the natural ends of my hands and mouth, but surely such things are not morally wrong?
        But, an NLT would agree because these sorts of examples are not cases of the faculty being used to “frustrate” the natural end of the hands or mouth. If on the other hand we wired someone’s jaw shut so they could not eat through the mouth, or if someone always walked on their hands even though they had perfectly good legs, then this might be different.5 But as it stands simply using a faculty for something other than what it is for is not the same as using that faculty to frustrate its end.
        Furthermore, the claim is not that if you use a faculty with the knowledge that it will be frustrated then it is wrong; it is that if you intend to use it to be frustrated. So, for example, sex between a man and women when the woman is pregnant is not wrong for the NLT.
        Also, the claim is not that if something is “unnatural” it is wrong. Deciding whether something is right or wrong is not the same as asking whether something is “man-made or not”. If this was the case, wearing glasses and taking medication would be wrong and the NLT is not committed to this. So the use of sex toys, or various medications such as Viagra is not wrong even though they are unnatural.
        We might think that linking sex to procreation in this way would take all the fun out of sex but this is not the case. Just as one can eat a dish in many different ways whilst always fulfilling the natural function of eating, one can be involved in different forms of sexual act, fantasy, etc. as long as it is part of the long term function of the sexual organs (so, for example, oral sex is not necessarily ruled out as long as it is, overall, part of a sex act that is intended for procreation).
        As noted, the NLT does, though, rule out homosexual sex and all forms of contraception because having sex whilst using contraception is to use the sexual faculties whilst intending to frustrate their end.
        The plausibility of this theory need not turn on how religious you are. We could give an atheistic evolutionary biological account that also talks about the “function” of our sexual faculties.
        There are many things which we could ask regarding this overall NLT approach to the ethics of sex. However, the main question to ask turns on why we might think that just because something is the case; namely, it is the function of sexual faculties to reproduce, that this is how things ought to be.
        This “is/‘ought” gap plagues many moral theories but seems particularly pressing here. Put simply, it does not seem problematic for someone using contraception to say: “true, I am intending to frustrate the natural function of my sexual faculties but why does that mean I ought not do it?”

    Summary of Natural Law Theory’s view on sex 

    Sexual Act/Activity Morally Acceptable Morally Unacceptable It Depends…
    Celibacy X    
    Oral sex     X
    Homosexual sex   X  
    Contraception   X  
    Premarital sex   X  
    Adultery   X  
    Masturbation   X  
    Sex toys     X
    Sadomasochism     X
    Viagra X    
    Pornography   X  
    Anal sex   X  
    Prostitution   X  

    4. Kant and Sex

    Kant thinks that sex is morally permissible within the context of a heterosexual, lifelong, and monogamous marriage. Any sexual act outside these contexts — homosexuality, masturbation, adultery, premarital sex — is morally wrong. His reasons for thinking this are very complex, not least because his writing on the subject, like just about all of his writing, is incredibly dense, but broadly speaking, his views on sex are based on his Second Formulation of the Categorical Imperative (see Chapter 2): act in such a way that you always treat humanity, whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end.
        Kant, like St. Augustine (354–430) and sometimes Freud, is what Alan Soble (1947–) calls a sexual pessimist (Plato and many modern philosophers would be counted as sexual optimists). The broad feeling amongst the pessimists is that our sexual desires and impulses, and acting upon those impulses, are undignified. The sexual part of our nature is unbefitting to how humans should behave and threatens our proper moral life.
        For Kant, sexual desire is the only impulse in us that takes the body of another human as the object of indulgence. Kant says regarding sexual appetite:

    Far from there being any concern for the happiness of the loved one, the lover, in order to satisfy his [sexual] desire and still his [sexual] appetite, may even plunge the loved one into the depths of misery […] [and after having sex] the person is cast aside as one casts away a lemon which has been sucked dry.6

    If you recall from Chapter 2, Kant believes that treating others as whole persons is key to being moral, but for him, this is precisely what is missing in sexual desires. That is, in sex we are treating others as objects and not treating them as whole persons and hence we are acting immorally. In the language of his second formulation of the Categorical Imperative: in having sex we are treating people merely as a means to an end. Consider this full expression of Kant’s sexual pessimism:

    Because sexuality is not an inclination which one human being has for another as such, but is an inclination for the sex of another, it is a principle of the degradation of human nature, in that it gives rise to the preference of one sex to the other, and to the dishonouring of that sex through the satisfaction of desire.7

    So if this is his general pessimistic view of sex how does that relate to a view on ethics? As it stands it looks like any sexual desire or act is going to be morally wrong, but if that is the case, then that means that for Kant the continued existence of the human race is evidence of immoral behaviour! That is surely wrong. Well, for Kant, the only reason it is not wrong is the role of marriage. In the context of marriage, and only in marriage, Kant thinks that sex and sexual desire is more than simply treating another merely as a means to an end. But why?
        First we must understand what Kant means by marriage:

    [Marriage] is an agreement between two persons by which they grant each other equal reciprocal rights, each of them undertaking to surrender the whole of their person to the other with a complete right of disposal over it.8

    So we can avoid the charge of objectifying and using a sexual partner merely as a means to an end because in sex within marriage you are treating each other as a whole person and thus there is reciprocity. Sex within marriage is about the whole person and not simply the genitals, sexual desire and pleasure. How does this work? This is how Soble starts to approach this question:

    But because the acquisition [of another through sex] in marriage is reciprocal, each person regains his or her personhood (and hence does not lose it, after all). When I “surrender” myself to you, and you thereby acquire me, but you also “surrender” yourself to me, and I thereby acquire you, which “you” includes the “me” that you have acquired, we each  urrender but then reacquire ourselves.9

    This reciprocity though is not present in non-marital sexual relationships. This is very hard to understand on many levels and we urge the reader not to get too caught up on this.
        We wanted to show you that Kant is complex and that the answers are not simple. The greatest Kant scholars are still not sure how to understand his ideas on sex. The thing to remember though is that via the second formulation of the Categorical Imperative Kant thinks that sex outside heterosexual marriage is wrong. Within marriage it is acceptable.

    5. Sex and Utilitarianism

    As you will recall from Chapter 1 Utilitarianism does not rule out an act on the basis of it being a particular act. This means that if Utilitarianism is correct we cannot say that any particular sex act is always wrong. Premarital sex, or homosexual sex, or masturbation, or oral sex can be morally acceptable. The matter is decided by whether or not performing that act brings about more pleasure overall than not doing so. This leaves a few questions and qualifications that need to be made.
        First, although sex will typically lead to pleasure that does not mean that Utilitarianism is committed to the claim that the act of having sex is always good. Utilitarianism does leave space for us to show that rape and paedophilia are morally wrong. For even though the rapist or paedophile might get pleasure from their act, it does not take much to see that the overall unhappiness, the mental and physical suffering of the victim, the distress of relatives and loved ones etc. is much greater because the act has taken place.
        Second, just because sex is typically pleasurable it does not mean Utilitarianism is committed to the claim that we have a duty to have as much sex as possible. For there are things we can do that bring about more overall happiness. Or we might suppose that having sex all the time might have detrimental effects on relationships and one’s mental and physical health.
        Third, for Utilitarianism, heterosexual sex within a marriage might be morally wrong if there has been coercion or threats, or just a general unhappiness with perfunctory sex, where almost any other activity would bring about more happiness. (Notice then the contrast with the Kantian and the NLT accounts).
        Fourth, adultery or having multiple sexual partners can be morally acceptable. We can imagine a case where, for example, the overall happiness is increased if a married couple agree to have sex with other people to keep their own marriage fun and interesting. Or we might think that someone who is generally not interested in, or does not have time for, a long-term relationship is happier with mutually consenting multiple sexual partners (or prostitutes).
        Fifth, Mill gives a different answer to Bentham to questions regarding what we ought to do when considering various sex acts because of his distinction between higher and lower pleasures. In general Mill did not value sex and he took the pleasures that arose from it to be fleeting and of lower value. This is because Mill thought that some pleasures are qualitatively distinct from others and thus outweigh other, lower, pleasures. Bentham however would not make this distinction (see Chapter 1 section 9).
        So if we keep this distinction in mind we might be able to distinguish between types of sex acts. Perhaps some sex acts are lower and some higher than others? We’ll leave the reader to think through some of the implications of this.

    6. Sex and the Virtue Theory

    Although virtue theorists do write about many applied ethical issues, they typically do not write about sex. Those that do (e.g. Elizabeth Anscombe (1919–2001), Peter Geach (1916–2013) and Roger Scruton (1944–)) often support a more conservative sexual ethic. However, there are a few (e.g. Raja Halwani (1967–)) who do not defend traditional accounts of sexual ethics and consequently, it is unhelpful to try and work out “the” virtue theory view on sexual conduct. So we will give the reader a framework to think through some issues that arise when you think about sexual ethics through the lens of virtue theory.
        If you recall, virtue theory is not a theory devised to help us make decisions. We cannot ask a virtue theorist: “how should we calculate what to do in this or that situation”? When faced with this sort of question, the virtue theorist will answer that you should do whatever a virtuous agent would do. But what is it to be virtuous? Well, the general idea is that to be virtuous is to develop certain dispositions or habits so that we respond to things in the world in the right way, at the right time, with the right reasons, to the right extent.
        To get a sense of this, recall the “Doctrine of the Golden Mean” from Aristotle (see Chapter 3 section 4). The idea here is that by acting between excess and deficiency regarding certain feelings we are acting rationally, that is, virtuously. If we keep doing this then we will develop a habit or disposition for this sort of action, and we will just get better at “seeing” what is required of us and responding in the right way in any particular situations. For instance, take “fear”.
        To have an excess of fear is to be cowardly whereas the lack of fear is to be rash or headstrong. To act rationally with regard to fear is to have the virtue of courage. The more we act courageously then the better we will be at having courage and thus will need less help from others in order to see what is courageous. We can repeat this for other virtues, e.g. the virtue of “generosity” would be the mean between stinginess and wastefulness.
        When discussing sexual ethics a number of different virtues might be relevant. In terms of an Aristotelian approach the virtue that is relevant is temperance (the vice being intemperance). This virtue is to do with our desires or appetites — this includes the desire for food, drink, and importantly for us, sex. A rough modern interpretation of this virtue would be “moderation”. The person who has the virtue of temperance will not either be a drunk or a glutton or be someone who is teetotal or who starves himself. In relation to sex, the agent who has the virtue of temperance will not simply be driven by unchecked sexual desires nor will he deny natural sexual desires completely but rather he will have sex at the right time, with the right people for the right reasons.
        One way of seeing if our action is intemperate is if our actions conflict with our other goals and virtues. One example is health. Someone who is intemperate with regard to sex (e.g. promiscuous) would potentially become unhealthy — perhaps physically and emotionally. Or consider other things we might value such as friendship or education: in these too we can imagine how intemperance might make these ends hard to achieve — e.g. just consider how a friendship would be wrecked or made impossible with constant unwanted sexual advances. There are some other things that the virtue theorist might say about sex.
        First, the virtue theorist would say that rape is always wrong because it violates the other person’s sexual autonomy which is the choice of when and how to have sex and with whom. Second, paedophilia is also always wrong for similar reasons. Adultery might be wrong because an intemperate person would break the marriage vows because of their sexual desire.
        So, like Utilitarianism, the answer to whether a virtue theorist would think a certain sexual activity is right or wrong will depend on whether a virtuous agent would do that act, and that would depend on whether the activity fitted within the Golden Mean.


    Philosophers since at least Plato have discussed sex as it raises a number of interesting philosophical questions. Sex is about relationships and interactions between people and consequently it seems to be a moral issue. Anyone that believes that sex is not a moral issue should ask themselves whether they think rape or paedophilia is morally wrong. However, when we move past such clear-cut cases, the issues become more subtle and complex.
        We considered a number of philosophical theories which give very different views. The Natural Law Theorist uses the idea of function and goal to ground a “conservative” view of sex. The Kantian also uses the idea of autonomy and respect for a person to ground a conservative view of sex, with a splash of pessimism about the unbefitting nature of sexual desire thrown in for good measure. Utilitarianism and Virtue Theory are less pessimistic and, as with their views on the other issues we have looked at in this book, more open to see what arises in different situations.     The two questions we leave you with are these. Having read this chapter, what do you think sex is? And how should moral theory guide our sexual practice?


    • Believing that Aquinas thinks that if sex doesn’t lead to pregnancy it is wrong.
    • Believing that for Aquinas sex has to be perfunctory and boring.
    • Thinking that the Utilitarian must think we should be promiscuous.
    • Not realizing that it isn’t clear what “sex” means.
    • Not realizing that how one defines “sex” will change how one answers moral questions.


    1. Imagine you were visited by an alien. The alien says “I’ve heard lot about ‘having sex’. What do you humans mean by this?” How would you respond?
    2. Do you think that sex is a moral issue? If so, what sorts of questions should moral philosophers consider in this area?
    3. Would the NLT think that using ear plugs or riding a bike were wrong? After all, they seem to frustrate the natural faculties of the ears and the legs.
    4. Could you be an atheist and be a NLT?
    5. In some countries same sex marriage is permissible. Do you think that in these countries Kant would say that homosexual sex is morally acceptable?
    6. Why does Kant think having multiple wives or husbands is morally wrong?
    7. Would you count Mill as a sexual optimist or pessimist?
    8. For Utilitarianism could bestiality be morally acceptable?
    9. What might Rule Utilitarianism (Chapter 1) say about some of these issues, e.g. whether adultery is morally right or wrong?
    10. How might Mill’s distinction between higher and lower pleasures be relevant in this context?
    11. What virtues and vices might be associated with sex?
    12. Use the Doctrine of the Golden Mean to think through the morality of a sexual activity.



    Natural Law Theory

    Doctrine of the Golden Mean



    Means and End


    Aristotle, The Nicomachean Ethics (Oxford: Clarendon Press, 1908), freely available at

    ‘Couple “Detained in UAE for Sex Outside Marriage”’, BBC News, freely available at

    Goldman, A. H., ‘Plain Sex’, Philosophy & Public Affairs, 6.3 (1977): 267–87.

    Halwani, R., The Philosophy of Love, Sex and Marriage: An Introduction (Oxford: Routledge, 2010),

    Mill, J. S., ‘Utilitarianism’, in Utilitarianism and Other Essays, ed. by Alan Ryan (London: Penguin Books, 2004).

    Milbank, John [@johnmilbank3], ‘There is no Need to Demand “Celibacy” in Gay Relationships. That Wrongly Equates Same Sex Physical Affection with Full (Heterosexual) Sex’,

    Bentham, Jeremy, ‘An Introduction to the Principles of Morals and Legislation’, in Utilitarianism and Other Essays, ed. by Alan Ryan (London: Penguin Books, 2004).

    ―, An Introduction to the Principles of Morals and Legislation, freely available at

    Roth, Philip, The Dying Animal (London: Random House, 2010).

    Soble, Alan, The Philosophy of Sex: Contemporary Readings (Plymouth: Rowman & Littlefield, 2002).

    ―, The Philosophy of Sex and Love: An Introduction (Paragon House, 1998).

    1  P. Roth, The Dying Animal, p. 69.

    2  Alan H. Goldman, ‘Plain Sex’, p. 49.

    3 ‘Couple “Detained in UAE for Sex Outside Marriage”’, BBC News, world-africa-39208946


    5 These examples are cited by Edward Feser here:

    6  I. Kant, Lectures on Ethics, cited in A. Soble, The Philosophy of Sex: Contemporary Readings, p. 200.

    7  Cited in ibid., p. 260.

    8  Ibid., p. 202.

    9  Ibid., p. 278.

    1.11: CHAPTER 10 SEXUAL ETHICS is shared under a CC BY license and was authored, remixed, and/or curated by LibreTexts.

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