Sexuality is always linked to a certain form of alterity. It entails the idea of an object lacking in the subject’s body, at every stage. Sexuality is the sharpest needle of the stimulus to think, or to imagine. Psychoanalytic theory always requires—in order to help it think about the complex formations of adults—reference to a historical point of view, which embodies recourse when analysis becomes too obscure or too convoluted. The sexuality of the two sexes is recognised there, but it must always be interpreted in a perspective at once retrospective and prospective. In fact, bisexuality can only be defined by referring, at the heart of each sex, to the other sex it always contains and with which it is in constant exchange. What Christian David terms accurately ‘bisexual mediation’ is so complex that it seems every opposition which the psyche can possibly experience or imagine is overqualified in the name of sexuality.