Sexual orientation, identity, and behavior
Bisexuality is romantic or sexual attraction to both males and females. The American Psychological Association states that "sexual orientation falls along a continuum. In other words, someone does not have to be exclusively homosexual or heterosexual, but can feel varying degrees of both. Sexual orientation develops across a person's lifetime–different people realize at different points in their lives that they are heterosexual, bisexual or homosexual."
Sexual attraction, behavior, and identity may also be incongruent, as sexual attraction or behavior may not necessarily be consistent with identity. Some individuals identify themselves as heterosexual, homosexual, or bisexual without having had any sexual experience. Others have had homosexual experiences but do not consider themselves to be gay, lesbian, or bisexual. Likewise, self-identified gay or lesbian individuals may occasionally sexually interact with members of the opposite sex but do not identify as bisexual. The terms queer, polysexual, heteroflexible, homoflexible, men who have sex with men and women who have sex with women may also be used to describe sexual identity or identify sexual behavior.
Some sources state that bisexuality encompasses romantic or sexual attraction to all gender identities or that it is romantic or sexual attraction to a person irrespective of that person's biological sex or gender, equating it to or rendering it interchangeable with pansexuality. The concept of pansexuality deliberately rejects the gender binary, the "notion of two genders and indeed of specific sexual orientations", as pansexual people are open to relationships with people who do not identify as strictly men or women. Sometimes the phrase "bisexual umbrella" is used to describe any nonmonosexual behaviors, attractions, and identities, usually for purposes of collective action and challenging monosexist cultural assumptions.
The bisexual activist Robyn Ochs defines bisexuality as "the potential to be attracted—romantically and/or sexually—to people of more than one sex and/or gender, not necessarily at the same time, not necessarily in the same way, and not necessarily to the same degree."
According to Rosario, Schrimshaw, Hunter, Braun (2006):
...the development of a lesbian, gay, or bisexual (LGB) sexual identity is a complex and often difficult process. Unlike members of other minority groups (e.g., ethnic and racial minorities), most LGB individuals are not raised in a community of similar others from whom they learn about their identity and who reinforce and support that identity. Rather, LGB individuals are often raised in communities that are either ignorant of or openly hostile toward homosexuality.
Bisexuality as a transitional identity has also been examined. In a longitudinal study about sexual identity development among lesbian, gay, and bisexual (LGB) youths, Rosario et al. "found evidence of both considerable consistency and change in LGB sexual identity over time". Youths who had identified as both gay/lesbian and bisexual prior to baseline were approximately three times more likely to identify as gay/lesbian than as bisexual at subsequent assessments. Of youths who had identified only as bisexual at earlier assessments, 60 to 70 percent continued to thus identify, while approximately 30 to 40 percent assumed a gay/lesbian identity over time. Rosario et al. suggested that "although there were youths who consistently self-identified as bisexual throughout the study, for other youths, a bisexual identity served as a transitional identity to a subsequent gay/lesbian identity."
By contrast, a longitudinal study by Lisa M. Diamond, which followed women identifying as lesbian, bisexual, or unlabeled, found that "more women adopted bisexual/unlabeled identities than relinquished these identities," over a ten-year period. The study also found that "bisexual/unlabeled women had stable overall distributions of same-sex/other-sex attractions." Diamond has also studied male bisexuality, noting that survey research found "almost as many men transitioned at some point from a gay identity to a bisexual, queer or unlabeled one, as did from a bisexual identity to a gay identity."
In the 1940s, the zoologist Alfred Kinsey created a scale to measure the continuum of sexual orientation from heterosexuality to homosexuality. Kinsey studied human sexuality and argued that people have the capability of being hetero- or homosexual even if this trait does not present itself in the current circumstances. The Kinsey scale is used to describe a person's sexual experience or response at a given time. It ranges from 0, meaning exclusively heterosexual, to 6, meaning exclusively homosexual. People who rank anywhere from 2 to 4 are often considered bisexual; they are often not fully one extreme or the other. The sociologists Martin S. Weinberg and Colin J. Williams write that, in principle, people who rank anywhere from 1 to 5 could be considered bisexual.
The psychologist Jim McKnight writes that while the idea that bisexuality is a form of sexual orientation intermediate between homosexuality and heterosexuality is implicit in the Kinsey scale, that conception has been "severely challenged" since the publication of Homosexualities (1978), by Weinberg and the psychologist Alan P. Bell.