Sexual behaviour (kàma or methuna) is any actions motivated by erotic desire and usually involving the genital region. This includes all forms of coitus, intercrural sex, masturbation, sexual fondling and perhaps even voyeurism. The third of the five Precepts, the basic principles of Buddhist ethics, says that one should avoid sexual misconduct (kàmesu micchàcàrà). What would make sexual (kàma) behaviour (càra) wrong (micchà)?
Once, while addressing an audience of brahmins, the Buddha said that intercourse with (1) girls under the guardianship of their parents (màturakkhità, piturakkhità), i.e. underaged; (2) women protected by Dhamma (dhammarakkhità), nuns or those who have taken a vow of celibacy; (3) married women (sassàmikà); (4) those undergoing punishment, (saparidaõóà), i.e. prisoners; or (5) those bedecked in garlands (màlàguõaparikkhittà), i.e. engaged to be married, would be wrong (A.V,264). Because this discourse was addressed to men, the Buddha spoke only of female sexual partners. Had he been addressing women, he would of course have spoken of male equivalents.
A child is unlikely to have the maturity or experience to make an informed decision concerning sex, while having sex with 2, 3 and 5 would involve them in breaking a solemn vow or promise, i.e. lying. An incarcerated person can be coerced into doing something they really do not wish to do and thus cannot make a genuinely free choice. It is clear from this that sex involving exploitation, dishonesty or coercion or that is in any way non-consensual, would be breaking the third Precept. Although not mentioned here, using or threatening physical force (i.e. rape) to compel someone to have sex, and intercourse with an intoxicated or a mentally disabled person, would also qualify as sexual misconduct. From the Buddhist perspective, therefore, sex before marriage, masturbation, homosexuality, with a person of a lower caste (forbidden in Hinduism) or sexual promiscuity, while perhaps being inadvisable, socially unacceptable or not conducive to spiritual development, would not per se be breaking the third Precept. Having a nocturnal emission does not break the Precept either.
As in many societies, sex in ancient India was surrounded by numerous superstitions, restrictions and taboos. Brahmins believed that having intercourse when one's wife was pregnant would defile the foetus (atimiëhaja) or when she was nursing, would make her milk impure and thereby negatively affect the baby (asucipañipãta). They taught that it was proper to have sex only to produce offspring but not for pleasure (kàma), for sport (dava) or out of sensual delight (rati). They also believed that it was wrong for a couple to have sex during the wife's menstruation (utunã). The Buddha commended brahmins who followed such rules, not because he agreed with them, but because they were being true to what they preached (A.III,226). Another widespread belief was that indulging in too much sex could cause various ailments and lack of judgment (Ja,VI,295). There are no examples of the Buddha subscribing to these or other sexual superstitions.
While accepting that sex is a normal part of lay life, the Buddha generally had a poor opinion of it. He dismissed it as `a village thing' (gàma dhamma, D.I,4), i.e. common, unsophisticated and worldly. He understood that a heightened desire for sensual pleasure (kàmacchanda) causes physical and psychological restlessness and that this diverts one's attention from spiritual aspirations and hinders meditation. He encouraged his more serious disciples to limit their sexual behaviour or to embrace celibacy (brahmacariya). Monks and nuns, of course, are required to be celibate. However, experience shows that taking a vow of celibacy when one is not ready for it can be anything but helpful. Constantly struggling against and denying sexual desire can create more problems than it solves and in fact can even be psychologically harmful. See Adultery, Incest and Prostitution.