One reasonable candidate is “the intention to produce sexual pleasure in oneself or in another”
sexual interest … [is] … an interpersonal sensitivity, one that enables us to delight in the mind and character of other persons as well as in their flesh… [S]ex may be seen as an instinctual agency by which persons respond to one anotherthrough their bodies. (Singer 1984: 382; see also Goldman 1977: 282–283; Russell 1929 [1970: passim])
.. a valuable thing in its own right, something to be cherished and promoted because it has intrinsic and gay hookups not merely instrumental value” (Soble, with Halwani 2017: 8).
1.2 Sexual Activity
It is difficult to define “sexual act” or “sexual activity.” Various proposed criteria face difficulties (Soble 2006a). This is especially so when closely related concepts (e.g., “having sex”) do not have the same extension. In ordinary language use, and according to some studies, people distinguish between having sex and sexual activity; they count many activities as sexual but not as having sex, such as solo masturbation, cyber-sex, and even oral sex (Soble 2006a: 15–16). Solo masturbation counts as sexual activity and as a sexual act, but not as having sex. There are a few criteria to define “sexual activity” (Soble 2006a). One criterion is reproduction: for an activity to be sexual it has to be or aim at being reproductive. This faces obvious counter-examples, such as same-sex sexual activities and heterosexual oral and anal sex (Soble 2006a: 18–19). Another criterion is bodily contact: sexual activities are those that involve contact with sexual body parts (though we need to figure out what these are). This fails as a sufficient condition (doctors sometimes have to touch patients’ genitals) and as a necessary one (achieving orgasm during a phone-sex chat) (Soble 2006a: 19–20).
Sexual pleasure is a third criterion: “Those activities … are sexual … which give rise to sexual pleasure” (Gray 1978: 191–192). But the production of sexual pleasure is not necessary because many acts do not produce such pleasure; and this criterion conceptually rules out non-pleasurable sex (Soble 2006a: 21–22). It might also not be sufficient: a man might see someone on the street and feel a twinge of sexual pleasure (Soble 1996: 130). The presence of sexual pleasure in this case does not suffice for the man’s experience to be sexual activity (perhaps if the man continues to look the experience becomes a sexual activity because of his intention to keep looking; Soble 1996: 130).
Another criterion is intention, though we need to figure out what the intention is for. But this is not necessary: two people who have sexual intercourse to procreate engage in a sexual act. The experience, if any, of sexual pleasure is a by-product of the action (Soble 1996: 132). This criterion is also not sufficient. Suppose that X intends to produce sexual pleasure in Y by “whistling ‘Dixie’,” but what X does is not a sexual act (Soble 2006a: 22).
sexual desire is desire for contact with another person’s body and for the pleasure which such contact produces; sexual activity is activity which tends to fulfill such desire of the agent. (Goldman 1977: 268)
The definition sounds right: what else is a sexual act if not one that satisfies or “tends to” satisfy sexual desire? But it faces counter-examples. A prostitute performing fellatio on a man does it (typically) not to satisfy or fulfill her sexual desire, but to make money. Nor does the act tend to fulfill her desire, for she might have none to be fulfilled. Thus satisfying sexual desire is not necessary for an activity to be sexual. Whether it is sufficient depends on what we mean by “satisfaction” or “fulfillment”. If it means “the desire is no longer felt for the time being” or “the desire is gone”, satisfying sexual desire would not be sufficient. Taking a cold shower, a powerful sleeping pill, or even just focusing on something else might get rid of the sexual desire, yet these activities are not sexual. If “satisfying sexual desire” means, “the desire achieves its goal” (which is sexual fulfillment), satisfying sexual desire by a particular activity would be sufficient for that activity to be sexual, but the definition becomes circular. The criterion of sexual desire, then, does not succeed in defining “sexual act”.