Sexuality and the Transsexual
Consider a person, Alec, who believes he was born into the wrong kind of body. He believes himself to be essentially female, despite his anatomy. Accordingly, he chooses to become the woman he inwardly perceives himself to be: he dresses in women’s clothes, wears make-up, and acts the part of a woman (but no surgery or hormone treatment). He feels his authentic female self in his new role. He now calls himself (or she calls herself) Alice and feels the better for it. After a while, Alice comes to the realization that she is a lesbian—a female homosexual. She decides to change her appearance into a more masculine image: she cuts her hair short, wears manly clothes, and acts like a man (in so far as she can). In this guise Alice frequents places where lesbians mingle and successfully hooks up with likeminded others, most of whom are regular women. Sexually, Alice performs in the standard male manner, this being what her anatomy demands. To all appearances Alice looks and behaves just like the old Alec. Question: is Alice homosexual or heterosexual? She seems heterosexual when you consider her anatomy and sexual behavior, but from the inside she feels herself to be a woman making love to another woman, and thus homosexual. A male body is interacting with a female body in the usual heterosexual fashion, and yet psychologically the person is a woman interacting with a woman. Is this same-sex sexual behavior or different-sex sexual behavior?
Neither alternative seems to capture the facts. If we dwell on the external appearances, we find heterosexuality; while if we look inside, we see homosexuality. Objectively, the erstwhile Alec is a straight male; subjectively, the new Alice is a committed lesbian. Which is it to be? It seems to me that the only answer can be “Both”. A single person is biologically heterosexual and psychologically homosexual. Generally these two attributes go together–your psychological sexuality tracks your biological sexuality—but in the case described the two come apart. In other words, we can’t deduce psychological sexuality from biological sexuality: Alice is a counterexample. She has it both ways: she is a heterosexual homosexual. She is partly heterosexual and partly homosexual. Not bisexual, mind you: she only has sex with women; the duality lies in her not in her partners. On the one hand, Alice is a biological male copulating only with females (both biologically and psychologically); on the other, she is a psychological female copulating with other females. She lives a dual existence: gay and straight, queer and ordinary. Some may say she has the best of both worlds; at any rate, she is familiar with both. Of course, the same is true if we switch genders: Joan may wish she were male and enacts her wishes, becoming John. In this new identity she discovers herself to be gay, i.e. John identifies as homosexual. But John has a female body and uses it accordingly. So John uses his female body to sleep with men: it may look like typical heterosexual sex, but from the inside the erstwhile Joan is a man sleeping with another man. John is both homosexual and heterosexual, and quite happy with the combination. He is attracted to people of the same sex as him considered psychologically, but his biological identity implies heterosexual sexual behavior. He feels himself to be a gay man, but his way of expressing this is to use his female body in the biologically indicated manner. 
Here is an even more challenging case: Percy has a very special psychological identity—he feels himself to be a woman who identifies as a man. At present he is simply a man with an unusual yearning, but he wishes to transform himself into something closer to his subjective identity. Accordingly, he transitions to a female persona by changing his clothes, manner, etc. Now Percy is a woman who wishes she were a man: call this person Pearl. Pearl would like to become a man, or so she says. Percy has achieved his wish, but Pearl has wishes of her own—she wants to become a man. Maybe she does, by adopting male accouterments: but then we are back where we started—a man who wishes he were a woman wanting to be a man. If Pearl decides she is a lesbian, is she a heterosexual or a homosexual? She is a woman sleeping with other women using a male body, but she also identifies as male: she is homosexual psychologically, heterosexual biologically, and also heterosexual psychologically (since she identifies as male while being psychologically female). It sounds like a very difficult psychological state to be in, and perhaps one that can never actually occur. But it shows what can happen when biological sexuality and psychological sexuality diverge in logically possible ways. We may need to reckon with far more complex forms of sexuality than the few forms currently recognized. Possible worlds may be sexually much richer than we can easily imagine.
 If you were to transfer the brain of a homosexual man into a woman’s body, you would get something like John: the brain would want men, while the female body would have to suffice for sexual relations.