temperament

Temperament comes from the Latin verb temperare: to mix, to combine, to proportion correctly. In medieval and ancient medicine, your temperament was the exact mixture of four humors—blood, phlegm, yellow bile, and black bile. An excess of one or another produced distinct personality types. Too much blood made you sanguine: optimistic, social, hot-blooded. Too much phlegm made you phlegmatic: calm, slow, heavy.

Galen, the Roman physician writing in the 2nd century CE, systematized these categories. The choleric person burned hot with yellow bile—passionate, quick-tempered, ambitious. The melancholic person was weighed down by black bile—introspective, pessimistic, analytical. For two thousand years, this theory of personality-as-chemistry dominated European medicine, philosophy, and even literature. Personality was not psychology. It was physics.

What seems strange now reveals something true about personality: it really is chemical. Medieval doctors without modern chemistry intuited what neuroscience now confirms—that mood, temperament, and personality correlate with brain chemistry, with hormones, with physiological balance. They used wrong categories and wrong substances, but they grasped the principle: you are what mixes inside you.

The word 'temperament' survives even though we've abandoned the humor theory. We still say someone has a fiery temperament, or a calm one. We still speak of temperamental people (those whose moods shift like unbalanced humors). The vocabulary persists because the insight was correct: personality is internal chemistry expressing itself outwardly. Medieval medicine was wrong about the humors, but right about the principle.