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Penetration refers to the insertion of a penis or other object into an orifice such as a mouth, vagina, or anus. Penetration is an element of sexual pleasure and reproduction as well as a symbolic action defining virginity, marriage, and sodomy.

Penile penetration of the vagina is the key element in the definition of sexual intercourse, which only occurs when a male penis penetrates a female vagina. There is no requirement about the depth or duration of penile penetration for penetration to have been accomplished. Other sites of penile penetration such as the mouth or the anus do not constitute sexual intercourse but do constitute sexual activity. The specific requirement of penile penetration makes the difference between legal definitions of rape (penile penetration of the vagina and, more recently, anus) and sexual assault (no penile penetration of the vagina), and between sexual practices deemed to be natural and proper (penile penetration of the vagina) and those categorized by more conservative groups as unnatural or perverse (any sexual activity other than penile penetration of the vagina). Because of the central role of the penis, sexual activity between women, although it may include penetrations by objects other than penises, has sometimes not been considered sexual intercourse.


To accomplish heterosexual sexual intercourse, a man's penis must be erect or hard enough to push through or penetrate the resistance offered by vaginal tissue. The natural lubrication afforded by the vagina aids penetration by making passage through the vagina easier. Penile penetration of the vagina often results in male orgasm, and the ejaculation of semen and may, by itself, also provoke female orgasm. Orgasm solely by penile penetration does not happen as often for females as for males. Because most of the nerves that stimulate female sexual response are located in the outer third of the vagina, deep penetration is not necessary for female sexual pleasure, although some women enjoy the sensations of deep penetration. Penetration may also stimulate the woman's G-spot, a region of the anterior vagina wall that arouses surrounding tissue.

The biological purpose of penile penetration is to enable the conception of a child by delivering sperm as close to a female egg as possible. Typical penile penetration of the vagina would enable the penis to deposit semen on the cervix, the opening to the vagina. Natural conception occurs most often as a result of penetration with ejaculation in the vagina, although occasionally pregnancies occur as a result of sperm contained in the drops of initial preejaculate deposited near the vaginal opening. Removing the penis after penetration but before ejaculation is a risky form of birth control, mostly because of the presence of sperm in the preejaculate.

The concept of penile penetration underwrites concepts of virginity as well as symbolic understandings of marriage as male and female becoming one through coitus. These concepts are phallocentric, or focused on the penis as the necessary agent in all sexual scenarios. Whether there has been penile penetration of the vagina defines virginity. A woman who has not been penetrated by a penis is a virgin. Because the first penetration often causes pain and bleeding, the presence of blood on sheets is considered to be a sign not only of virginity but also of a successful penetration.

In coitus, the penis is understood as literally entering the woman's body, attaching the two people. This sense of physical unity then also sustains understandings of marriage as a physical uniting of a male and a female and of adultery as the invasion of that unity. The apparent complementarity of penis and vagina suggests the natural inevitability of penile penetration in heterosexual intercourse while simultaneously suggesting that other modes of penetration are unnatural, even though such practices, such as penile penetration of the anus or digital penetration of the vagina, involve equally complementary parts of the anatomy.

The penis may also penetrate parts of the body other than the vagina. Penetrating the mouth as in fellatio or the anus as in anal intercourse (also known as sodomy) were traditionally understood as unnatural in the logic that defined penetration as occurring only in a vagina. Such penetration can occur between males and females as well as between males and males and males and members of other species. Although such penetrations have long been a part of human sexual practice, they were repressed and gradually criminalized after the rise of Christianity. In 2003 a Texas law criminalizing sodomy and oral sex was deemed unconstitutional by the Supreme Court in Lawrence v. Texas. In the United States most sexual practices involving consenting adults are no longer criminalized.

Forced penile penetration of another without consent defines the crime of rape. Although rape originally occurred only between males and females who were not their wives, the definition of rape has been gradually expanded to include any kind of forced penile penetration of the vagina. Sexual assault occurs when there is any kind of forced sexual activity short of penile penetration of the vagina, including contact between the penis and the mouth or anus of another. Forced penile penetration of the anus of other males has been included as a form of rape.

Penile penetration is difficult if a male has difficulty achieving or sustaining an erection. Such failure is called erectile dysfunction. Several drugs on the market help remedy erectile dysfunction, including Viagra and Cialis. Other cures for the inability to penetrate include penile implants that stiffen the penis mechanically.

Rough or forced penetration can also cause injury to the one being penetrated. Tears in the vagina and anus can occur when a penis is too large, is inserted without adequate lubrication, or is pushed beyond normal anatomical limits.


Most notions of penetration are phallocentric or focused on the penis as a necessary element. Sexual penetrations, however, also occur with objects other than a penis. Dildos, which have existed since prehistory, are objects designed to penetrate both the vagina and the anus. Dildos, which often look like penises or have a long, cylindrical shape, are used by both females and males. Some lesbians use dildos, which strap on to one participant's body. Some dildos include an attachment to stimulate the G-spot. Others have two heads and are used for simultaneous penetration by two women. Smaller dildos, called butt plugs, are designed to penetrate the anus. People have also used other objects ranging from cucumbers and carrots to light bulbs as instruments for penetration, although some of these objects can cause injury.


Anand, Margot. 2000. Sexual Ecstasy: The Art of Orgasm. New York: Tarcher.

Cohen, Joseph. 2004. The Penis Book. New York: Broadway.

Lawrence v. Texas, 539 U.S. 558; 123 S. Ct. 2472 (2003).

Semans, Anne. 2004. The Many Joys of Sex Toys: The Ultimate How-to Handbook for Couples and Singles. New York: Broadway.

Underwood, Steven. 2003. Gay Men and Anal Eroticism: Tops, Bottoms, and Versatiles. New York: Harrington Park Press.

                                                Judith Roof