A Theory of Balance
For much of the Middle Ages, educated Europeans believed that the human body contained four main fluids, called humors, and that health depended on their balance. The Latin word humor simply meant fluid. The four were blood, phlegm, yellow bile (often called choler) and black bile (called melancholy). When they were in proportion, a person was well. When one dominated or became corrupted, discomfort, illness or a particular temperament was said to follow.
This article describes the theory as a general picture of the body and character. How physicians actually used it to diagnose and treat patients is covered separately. And, to be clear, it is not a guide to anything one should do today: modern medicine does not recognize these fluids as described.
Origins
The idea has Greek roots. Texts attributed to the Hippocratic tradition discuss bodily fluids and their balance, and the physician Galen, who worked in the Roman Empire in the second century, developed and systematized the scheme. Exactly how much belongs to Hippocrates himself, and how much to later writers, is debated by historians, so it is safest to say that humoral thinking grew over several centuries.
It reached medieval Europe through several routes: Latin summaries of Galen, Byzantine and Arabic medical writing, and the translation movement of the eleventh and twelfth centuries. Scholars at centers such as Salerno, and later the medical faculties of universities, taught the theory as part of a standard curriculum. Arabic authors, including Ibn Sina, restated and organized it, and their works were widely read in Latin.
The Four Humors and Their Qualities
The humors were attached to the same qualities as the elements, which tied the body to the cosmos.
| Humor | Qualities | Element | Season | Temperament |
|---|---|---|---|---|
| Blood | hot and wet | air | spring | sanguine |
| Yellow bile | hot and dry | fire | summer | choleric |
| Black bile | cold and dry | earth | fall | melancholic |
| Phlegm | cold and wet | water | winter | phlegmatic |
Charts like this appear in many manuscripts, often as circles or diagrams linking the humors with the four elements and the cycle of seasons. Some versions added ages of life, planets, times of day and even colors or tastes. Which phase of life belonged to which humor varied between authors, and the neat sets should be read as teaching devices more than as strict rules. Later medieval ideas of the ages of man often borrowed this fourfold pattern.
What Each Humor Was Thought to Do
Blood was considered the most beneficial humor, nourishing the body and associated with warmth, vigor and good cheer. Phlegm, cold and moist, was linked to the brain and to bodily fluids like mucus and saliva, and in excess to sluggishness. Yellow bile was thought to be produced in the liver and associated with quick temper and heat. Black bile, the most puzzling, was described as a dark, cold, dry residue, associated with the spleen and with gloom or deep thought.
No one could see black bile in a patient as a distinct substance, which is one reason modern historians treat it as a conceptual rather than an observed category. Medieval writers described dark vomit or stool as evidence, but the explanation remained partly speculative.
Temperament and Character
The theory also became a way to talk about personality. Everyone was thought to have a natural mixture, or complexion, and the usual dominant humor gave rise to a temperament:
- The sanguine person was imagined as cheerful, sociable and ruddy.
- The choleric person as quick, ambitious and irritable.
- The melancholic person as thoughtful, serious and prone to sadness.
- The phlegmatic person as calm, slow and steady.
These types shaped how writers described characters in literature and art. A poet might signal a character’s nature by listing a humor, and artists sometimes showed the four temperaments as figures in a set. The influence was long: words such as “sanguine,” “choleric,” “melancholy” and “phlegmatic” survive in English, though their meanings have shifted.
Gender, age and region were also thought to affect the mixture. Men were generally described as hotter and drier, women as colder and wetter, a view that fed into medieval ideas about female bodies. The old were thought to cool and dry with age, and children to be warm and moist. These claims reflect the assumptions of the theory, not observed facts, and later science has not supported them.
Why the Theory Lasted
Humoral thinking was persuasive for several reasons. It was coherent: one system tied the body to seasons, diet, the elements and personality. It offered explanations for ordinary experience, such as feeling sluggish in winter or heated in summer. It also fit with the authority of respected ancient texts, which medieval universities treated as foundations to be explained and refined, not dismissed.
It was also adaptable. Scholars debated how many humors there really were, whether other fluids like sweat or milk counted, and how digestion transformed food into blood. Those arguments show a living field of inquiry within its premises.
Limits and Legacy
The theory is not supported by modern anatomy or physiology. Dissection, the discovery of circulation, germ theory and chemistry all eventually undermined it, though the process took centuries and the language lingered. In the Middle Ages, though, it was a serious attempt to understand health, and it influenced how people thought about food, climate, emotion and moral character.