An idea about balance
The four humours theory held that the body contains four basic fluids, and that health depends on their proper proportion and mixture. The fluids were blood, phlegm, yellow bile and black bile. When they were balanced, a person was well. When one was in excess, in deficit or poorly mixed, illness resulted. This model dominated medical thinking in the Greek and Roman worlds and, in modified forms, in the medieval Islamic world, including centres such as Abbasid Baghdad, and in Europe for well over a thousand years.
It is important to note that the theory was never one fixed doctrine. Ancient authors used it in different ways, and some argued about the number and nature of the humours. The version in the textbooks is the one that later became standard.
Where the idea came from
The Hippocratic writings contain several explanations of disease. Some blame air, or heat, or a single substance. The treatise On the Nature of Man is the best-known early text to set out the four-humour scheme, arguing that the body is composed of blood, phlegm, yellow bile and black bile and that health is their balanced mixture. Tradition associates this work with Polybus, a pupil or son-in-law of Hippocrates, though authorship is uncertain.
The theory drew on a broader habit of Greek thought: explaining the world through a small number of basic principles in balance. Early natural philosophers discussed opposites such as hot and cold, wet and dry. This style of reasoning appears in the speculations of the Presocratic thinkers, and the four elements theory of earth, air, fire and water provided a ready model for dividing the body into four parts as well. The humours were not simply identical to the elements, but the two schemes were often linked.
The qualities and the seasons
Writers connected each humour with a pair of qualities and a season. The usual scheme, found in later authors, runs as follows:
| Humour | Qualities | Season | Associated element |
|---|---|---|---|
| Blood | hot and wet | spring | air |
| Yellow bile | hot and dry | summer | fire |
| Black bile | cold and dry | autumn | earth |
| Phlegm | cold and wet | winter | water |
This table represents a later standard presentation, and individual ancient writers varied. The point was that illness often followed the seasons, so a physician expected certain disorders in particular times of year. The Greek seasonal calendar and medicine thus shared a vocabulary.
From diagnosis to treatment
The theory was practical because it linked diagnosis to action. If a patient’s condition appeared to be too cold and wet, a physician might suggest warming and drying foods, rest, baths or drugs with the opposite qualities. The guiding principle was that opposites correct opposites. Other treatments aimed to remove an excess. Bloodletting, purging, vomiting and induced sweating were all used for this purpose, though the Hippocratic authors also urged restraint and attention to the patient’s strength.
Diet was a major tool. Foods were classified by their qualities, so that a physician might adjust meals according to age, season, occupation and constitution. Patients differed too: people could be thought naturally to have more of one humour, which linked the theory to descriptions of temperament, a connection developed more fully in later centuries.
Galen and the Roman world
Galen, working in the second century CE, gave the theory its most influential form. He combined the humours with the qualities, with ideas about the organs and with the philosophy of Plato and Aristotle, building a comprehensive system that covered physiology, drugs and treatment. His authority ensured that humoral reasoning became the default framework for physicians in the Roman Empire and its successor cultures.
Not all ancient physicians accepted the humours. Rival medical groups, such as the Methodists, explained disease through general states of the body’s tissues, and others emphasised experience over theory. The humoral approach was strong, but it was never uncontested.
Why it persisted
The theory lasted for a number of reasons. It was flexible: nearly any symptom could be assigned to some imbalance. It was coherent, connecting body, diet, climate and character in a single framework. It also produced treatments that felt logical and that sometimes coincided with sensible care, such as rest, fluids and attention to diet. And with no microscope, no concept of germs and no experimental method able to test the claims, there was little to contradict it.
The theory declined gradually. Anatomical studies of the sixteenth century, the demonstration that blood circulates, cell theory and germ theory in the nineteenth century slowly replaced it. Some of its language survives in everyday speech, in words such as “melancholy” (from “black bile”) and “phlegmatic”.
What to take from it
It is easy to dismiss the four humours as mistaken, and as a description of the body they were. But they were a serious attempt to explain illness in natural terms, by reasoning from observed patterns, and they allowed physicians to organise a huge range of experiences. They are best understood as a historical framework, not as a guide to health today.