The repressive hypothesis gives a clear account of how sex has been regarded since the 18th century: it explains how discourse on sexuality has been controlled and confined, and how that has been in the interests of the bourgeoisie. Foucault, however, is not satisfied with this hypothesis, and this book stands as a compelling attack on it. However, his attack does not simply consist of saying the hypothesis is wrong and taking a contrary position. Rather, it consists of taking a step back, and seeing where this hypothesis comes from, and why.
Foucault recognizes the repressive hypothesis itself as a form of discourse. We have developed a whole framework in which to talk about the ways in which bourgeois society represses our sexual impulses. We have developed a way of talking about how we are prevented from talking about sex. We have come to talk about our need to break free from this repression, to talk freely about sex and to enjoy sex, as a part of a larger political rebellion against bourgeois society.
Just like any other form of discourse, the repressive hypothesis is not simply a set of facts in a vacuum. It forces a Marxist reading of history: one where sexual repression is part of a larger history of class struggle. More important to Foucault than whether or not the repressive hypothesis is true is how the repressive hypothesis is formulated and why. Why is it so important to us to talk about sex, why do we have to insist that we are rebelling in doing so, and why do we insist on seeing that rebellion as part of a larger, political rebellion? Foucault sees this discourse as just a surface manifestation of a deeper will, a will to a certain kind of knowledge and a certain kind of power. His investigation wants to dig beneath the hypothesis itself and find what motivates it.