Foucault on Sexualities

as explained by David M. Halperin (2002):

“Sex takes on new social and individual functions, and it assumes a new
importance in defining and normalising the modern self. The conception of the
sexual instinct as an autonomous human function without an organ appears for the
first time in the nineteenth century, and without it our heavily psychologised
model of sexual subjectivity […] is inconceivable. Sexuality is indeed, as
Foucault claimed, a distinctively modern production."

“The nineteenth-century disciplining of the subject, though it purported to aim
at the eradication of ‘peripheral sexualities,’ paradoxically required their
consolidation and ‘implantation’ or ‘incorporation’ in individuals, for only by
that means could the subject’s body itself become so deeply, so minutely invaded
and colonised by the agencies of normalisation."

> 19th century laws against and medical marginalisation of 'homosexuals' actually played an important role in creating a homosexual self-conception ("a homosexual subjectivity" as it is called).

“It is only lately, Foucault emphasises […] that it has become almost impossible
simply to pursue the pleasures of homosexual contact ‘just so, when you felt
like it, every once in a while, or in phases’ […], without being forced to
deduce from one’s own behaviour that one is homosexual, without being
interpellated by the culpabilising category of ‘the homosexual’.”

What Foucault does/invites us (historians) to do

“is a question of systematically defining different historical forms of sexual
experience – different ways of being, different sets of relations to others and
to oneself, different articulations of pleasure and meaning, different forms of
consciousness.”

> each historical period and place has it own forms of sexuality, its own sexual idenitities.

These thoughts mainly belong to the later Foucault, i.e. after the publication in 1976 of the first volume of his History of sexuality (La volonté de savoir).

I suggest that any of these statements on homosexuality apply equally well to heterosexuality, as the latter is just as much a cultural construction as the former (although not marginalised).

For clarifications you can have a look at a glossary of Foucauldian terms and ideas, or you can read a very short summary of some of his ideas bearing on sexuality, identity, and power-knowledge (which also features a nice tour through "Foucault's Paris"!).

And even these postmodern, academic discussions, Lewis Carroll has eerily foreseen:

“Who are you?” said the Caterpillar.
This was not an encouraging opening for a conversation. Alice replied, rather shyly, “I—I hardly know, Sir, just at present—at least I know who I was when I got up this morning, but I think I must have changed several times since then.”
“What do you mean by that?” said the Caterpillar, sternly. “Explain yourself!”
“I can’t explain myself, I’m afraid, Sir,” said Alice, “because I’m not myself, you see.”
“I don’t see,” said the Caterpillar.
“I’m afraid I can’t put it more clearly,” Alice replied, very politely, “for I can’t understand it myself, to begin with; and being so many different sizes in a day is very confusing.”
“It isn’t,” said the Caterpillar.
“Well, perhaps you haven’t found it so yet,” said Alice; “but when you have to turn into a chrysalis—you will some day, you know—and then after that into a butterfly, I should think you’ll feel it a little queer, won’t you?”