humoral theory
a former theory that explained physical and psychological health or illness in terms of the state of balance or imbalance of various bodily fluids. According to Greek physician Hippocrates (5th century bce), health was a function of the proper balance of four humors: blood, black bile, yellow bile, and phlegm (the classical humors or cardinal humors). This idea was also used to explain temperament: A predominance of blood was associated with a sanguine type; black bile with a melancholic type; yellow bile or choler with a choleric type; and phlegm with a phlegmatic type. Galen did much to preserve and promulgate this explanatory approach, which survived well into the 17th century. Humoral theory provides psychology with its earliest personality typology, as well as an early model of the relation between bodily and psychological states.