The Four Humors. Humorism was an ancient theory of medicine that held that an excess or deficiency of any of four distinct bodily fluids, or 'humors', directly influences a person's temperament and health. From Hippocrates onward, the humoral theory was adopted by Greek, Roman and Persian physicians, and became the most commonly held view of the human body among European physicians until the advent of modern medical research in the nineteenth century. The four humors are black bile, yellow bile, phlegm, and blood. Each corresponds to one of the traditional four temperaments or personality types: sanguine (pleasure-seeking and sociable), choleric (ambitious and leader-like), melancholic (analytical and literal), and phlegmatic (relaxed and thoughtful). Engraving by Virgilius Solis, the Elder, 16th century. This image has been color-enhanced.