Full context:   Temperament theory has its roots in the ancient theory of humourism. It may have originated in Mesopotamia, but it was Greek physician Hippocrates (460–370 BC) (and later Galen) who developed it into a medical theory. He believed that certain human moods, emotions, and behaviours were caused by an excess or lack of body fluids (called "humours"), which he classified as blood, yellow bile, black bile, and phlegm, each of which was responsible for different patterns in personalities, as well as how susceptible one was to getting a disease. Galen (AD 129 – c. 200) developed the first typology of temperament in his dissertation De temperamentis, and searched for physiological reasons for different behaviours in humans. He classified them as hot/cold and dry/wet taken from the four elements. There could also be balance between the qualities, yielding a total of nine temperaments. The word "temperament" itself comes from Latin "temperare", "to mix". In the ideal personality, the complementary characteristics were exquisitely balanced among warm-cool and dry-moist. In four less-ideal types, one of the four qualities was dominant over all the others. In the remaining four types, one pair of qualities dominated the complementary pair; for example, warm and moist dominated cool and dry. These last four were the temperamental categories which Galen named "sanguine", "choleric", "melancholic", and "phlegmatic" after the bodily humours. Each was the result of an excess of one of the humours which produced the imbalance in paired qualities.