In tracing the genealogy of sexuality to the nineteenth century marriage of science and confession, Foucault points out how temporary our modern concept of sexuality is. He lists five ways that science and confession were brought together, creating a special kind of discourse around sexuality that focuses on a controlled and systematized extraction of a confession. The discourse of science leads us to think of sexuality as a scientia sexualis, an object of detached, scientific study, about which we can gather objective data and facts. Sex becomes an object of knowledge, something we can understand, control, and use. The discourse of confession leads us to think of sexuality as something hidden, something secret, and something shameful. These two discourses combine to form a concept of sexuality as a mystery, something hidden within us that must be drawn out, and that also can be codified into knowledge. As knowledge hidden within us, our sexuality becomes the key to understanding who and what we are.
Foucault asserts that there is nothing about our sexual desires or behaviors themselves that should make us think that they express profound truths about us. Rather, he argues, it is the discourse we have built up around those desires and behaviors that suggest the profound truth. Our concept of sexuality as fundamental to human nature has more to do with the contingent evolution of our discourses than with the actual facts of the matter. As such, Foucault is one of the first constructivists regarding sexuality. That is, he regards sexual categories as contingent human constructions. On the opposite side of this debate are the essentialists, who argue that our sexual categories are fixed, that we are actually drawing on objective, scientific facts when we make distinctions. This debate is by no means settled, and the essentialist camp certainly holds a defensible position. We might grant Foucault, for instance, that our discourse on sexuality is shaped by historical contingencies while still maintaining that the concepts used in this discourse are objective and universal. Just because ideas are expressed in a certain way and in a certain context does not necessarily mean that those ideas are not valid outside that context.