The core idea
Most learned medicine in the Middle Ages rested on the theory of the four humors, inherited from ancient Greek writers and elaborated by Galen and later Arabic authors. The body was thought to contain four main fluids: blood, phlegm, yellow bile (or choler) and black bile (or melancholy). Health meant these were in proper balance, and illness meant a surplus, deficiency or corruption of one or more.
This was not a fringe belief. It was the shared framework taught in universities and used by physicians across Europe, and it influenced advice on food, exercise, bathing, bloodletting and drugs. The theory itself is covered in more detail in material on humoral medicine, so this article concentrates on how it worked in diagnosis and care.
Qualities and links
Each humor was associated with a pair of qualities. Blood was warm and moist, phlegm cold and moist, yellow bile hot and dry, black bile cold and dry. The qualities in turn linked to the four elements, to the seasons, and to stages of life. Blood was tied to spring and childhood, yellow bile to summer and youth, black bile to fall and middle age, and phlegm to winter and old age, though sources do not all agree on details. The cycle of seasons and the ages of man were thus part of the same pattern, which gave the theory its sense of order.
Temperament
People were thought to differ in their natural balance, called complexion or temperament. A person with a lot of blood was sanguine: cheerful, sociable and ruddy. An excess of yellow bile made one choleric, quick-tempered and lean. Phlegm produced a phlegmatic, calm and slow person, and black bile a melancholic, thoughtful and gloomy one. These labels were not just descriptions of mood. They affected which treatments suited a person, and a remedy that was good for a cold, moist child might be wrong for a hot, dry elderly man.
The temperament labels survive in modern speech, though our use of them is much looser than the medieval one.
How a physician diagnosed
Diagnosis aimed to work out which humor or quality was out of balance. The physician collected several kinds of information:
- History and appearance. Age, sex, occupation, season, diet and habits, as well as skin color, build and manner.
- Pulse. Its speed, strength and rhythm were interpreted using elaborate descriptions inherited from Galen.
- Urine. Uroscopy was the best-known method. The physician looked at the color, clarity, sediment and layers of the urine in a flask, often comparing it to a chart or wheel of colors. It was so closely associated with doctors that the urine flask became their symbol in art.
- Stool, sweat and other discharges, as well as the course of the illness over days.
The doctor often relied on the patient’s account and on messengers carrying a urine sample, so diagnosis at a distance was common. Critics even in the Middle Ages complained that doctors were over-reliant on urine.
From diagnosis to treatment
The guiding rule was that opposites cure opposites. A condition judged hot and dry, such as a fever, would be treated with cooling and moistening foods and drugs. A cold and moist illness, such as a heavy cough with phlegm, called for warming and drying remedies. Medicines were classed by their qualities and by degrees of strength, from mild to very strong, which let physicians combine ingredients to hit a target.
If the problem was thought to be an excess of a humor, the treatment might remove it, through bloodletting, purges, vomiting or sweating. If a humor was thought to be corrupted or “unripe,” practitioners watched for signs that the body was “cooking” it, such as changes in the urine, and waited. Some conditions had critical days on which the illness was expected to turn, which linked to astrological reasoning.
The overall approach was to support the body’s own efforts, an idea often expressed in the saying that nature is the healer, and to avoid forcing matters. Learned physicians frequently urged caution.
Variations and critics
The humoral system was not rigid. Different authors weighted the humors differently, argued about the role of the heart and brain, and added explanations such as bad air, or miasma, for epidemics. Ibn Sina’s Canon systematized the theory and was highly influential in Latin translation. Physicians also disagreed about particular drugs and about how much to trust ancient authorities versus experience.
The theory also had practical limits. It could explain nearly any outcome after the fact, which made it hard to test and correct. Its principles, such as the danger of an unbalanced diet and the value of rest, sometimes led to helpful advice, but it gave no real route to understanding infection. When the Black Death struck, the framework offered bad air and planetary influences as causes, and its remedies could not stop the epidemic.
What the theory shows about medieval thinking
The humoral system reveals how medieval people connected the body to the cosmos. The same four qualities appeared in the elements, in the seasons and in the planets, so understanding one part of the world helped to understand the others. That made medicine a branch of natural philosophy, studied alongside logic and astronomy, and gave physicians their intellectual authority. It is an elegant system, even though modern medicine has replaced it.