Fig. 1.

The four humors and dimensional reasoning. The figure depicts a classic version of the four humors (the fundamental fluids of the body: blood, yellow bile, black bile, and phlegm), with the organ to which each was most closely associated and the personality type corresponding to each humor. Health, physical and mental, was a consequence of a balance of the humors. The two axes, wet-dry and hot-cold, describe the essential qualities of each humor. Each humor was also identified with an element (air, fire, earth, and water). Various philosophers and physicians over the centuries substantially elaborated and modified this basic theory.