Foucault shows the different kinds of madness in classical thought. He first discusses madness and melancholia. The idea of melancholia was fixed in the sixteenth century. Its symptoms were the ideas that a delirious person formed about himself. Up to the seventeenth century, discussions of melancholia remained fixed within a tradition of the four humors. But debate began over the origin of melancholia. This debate resulted in a causality of substances being replaced by a movement of qualities. Qualities, which can be affected by circumstances, organized and integrated melancholia. Foucault discusses various humoral and spiritual explanations of melancholia. The theme of partial delirium disappeared, and was replaced by qualitative data like sadness, solitude and immobility.
Analyses of mania followed similar principles to analyses of melancholia. Mania was opposed to melancholia, but both were believed to be due to a movement of animal spirits. In the eighteenth century, though, the image of animal spirits was replaced by the image of tension in nerve fibers. Objects did not present themselves as "real" to the maniac. A psychological explanation replaced ideas of humors and tension. Willis (an English physician) was responsible for discovering the alternation of mania and melancholia. Most eighteenth century physicians acknowledged the similarity between mania and melancholia. The study of melancholia began with observation and then explained images. Images were the starting point for study, and their organizing force made the structure of perception possible.
Foucault then discusses hysteria and hypochondria. Two problems arise in analyzing these qualities. To what extent are hysteria and hypochondria madness? And, are they a couple, like mania and melancholia? The two were rarely classified together, but slowly began to be seen as same disease. During the classical period, hysteria and hypochondria slowly became seen as mental diseases. Two essential lines of development existed in the classical period for hysteria and hypochondria. Firstly, the illnesses were united to form the concept of a "disease of the nerves." Secondly, they were integrated into "diseases of the mind." But classical physicians could not discover the particular qualities of hysteria and hypochondria.
Hysteria progressed and assumed its dimensions in the space of the body. Classical physicians saw the problem as identifying the system through which disease dispersed itself. By the eighteenth century nothing remained of the idea of the mobility of the womb except the theme of corporeal space. In the eighteenth century the idea of the dynamics of corporeal space changed to a morality of sensibility. The evolution of this theme had three stages; the dynamics of organic and moral penetration; the psychology of corporeal continuity; and the ethic of nervous sensibility.
The disordered movement of hysteria and hypochondria was believed to result from the disordered movement of animal spirits. Hysteria was a deceptive disease because it had various symptoms. Doctors said that it affected women more because they had "softer" bodies. The idea that the womb "rose" above its place was replaced by the belief that spirits moved chaotically within the body. A body that is penetrated by disease must also be continuous. This problem haunted eighteenth century medicine. It would make hysteria and hypochondria diseases of the general agency of all sympathies. The nervous system was used to explain the body's sensibility with regard to its own phenomena. The sympathetic sensibility of women predisposed them to the "vapors" and nervous disease.
Foucault asks what sympathy is. To understand classical conceptions of sympathy, it is important to understand the idea of irritated nerve fibers. It was believed that too much sensibility resulted in unconsciousness or nervous shock. One could fall ill from too much exposure to outside, worldly stimulation. As a result, people were both more innocent and more guilty. They were guilty because their lifestyle and passions irritated their nerves. The innocence of the nervous sufferer was seen as evidence of a deeper guilt and its punishment. On the threshold of the nineteenth century, the view that hysteria and hypochondria were mental diseases remained. However, by the distinction between sensibility and sensation, they were associated with unreason, characterized by blindness. Once the mind became blind, through an excess of sensibility, madness appeared. Madness acquired a content of guilt, moral sanction and just punishment. The manifestation of non-being became the natural punishment of moral evil. Psychology and morality now contested the same domain. Nineteenth century scientific psychiatry was now possible.