This is Foucault's first analysis of the different conditions and syndromes seen by the eighteenth century as forming madness. He analyzes two sets of ideas that were held in opposition to each other. Both involve body and mind in different ways. Foucault explores the way in which doctors and theorists of madness describe the causes and effects of mental illness. In doing so, Foucault delves into the history of medicine.

Foucault's definition of melancholia is unique, and does not refer to depression. A melancholic person could have a range of delirious symptoms, including unreal or false beliefs, combined with an otherwise normal personality. The tradition of humors that Foucault discusses was a central part of early modern medicine. Doctors believed that there were four humors—blood, phlegm, choler and black bile—which corresponded to the four elements of fire, water, air and earth. Different personality types had a different balance of humors; the melancholic personality had too much black bile. The doctor's task was to balance out the humors.

The shift that Foucault describes is a subtle one. Instead of believing that melancholia was caused by an imbalance of physical substances (humors) within the body, classical doctors now believed that melancholia could be caused by the patient's mental state. Foucault describes the narrowing down of a condition and the establishment of firm definitions.

A similar process occurred with the concept of mania. Whereas melancholics could have a range of symptoms, maniacs were highly excitable, wild and uncontrollable. Doctors came to realize that mania was the exact opposite of melancholia. Foucault charts a change in medical thought, from the emphasis on animal spirits to an emphasis on tension within the nervous system. Another key shift was the idea that the two conditions alternated within one person. As medical understanding developed, they became more closely linked.

The discussion of hysteria and hypochondria centers on the idea of mental disease. Mental disease is a condition affecting the mind that is treated by doctors and that has recognized symptoms. Madness, on the other hand, is a state of being linked to unreason that has a complex relationship with reason itself.

Hypochondria is falsely believing yourself to be ill; hysteria is essentially a disease of spasm, convulsion and over-excitement. It is particularly common in women. From ancient medicine onwards, it was seen as relating to the uncontrolled movement of the womb within the body. The word hysteria is derived from the Greek word for "womb".

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