Ideas About the Cause of Disease

These ideas were not necessarily alternatives. A person could believe that God had sent an illness while also accepting a physician’s explanation that their bodily humours were unbalanced. Understanding this overlap helps explain why religious beliefs and ancient medical theories remained influential together.

Religion: illness as God’s will

The Christian Church was central to medieval life. Its ceremonies marked birth, marriage and death, and priests taught people about sin and salvation. Many people could not read, so the Church was an important source of knowledge and authority.

People believed that illness could be God’s will or a punishment for sin. Leprosy, for example, could be interpreted as divine punishment. This gave disease a moral explanation: illness might reflect a person’s relationship with God rather than simply a problem within their body. This was a belief about disease, not evidence that someone who became ill had done something wrong.

Astrology: the influence of stars and planets

Astrology offered another explanation beyond ordinary bodily processes. People believed that the positions of stars and planets could influence health. Physicians consulted star charts and considered when a patient had been born to help diagnose illness.

Astrology also overlapped with the Four Humours. For example, Capricorn, Aquarius and Pisces were associated with excess phlegm. Although the Church disapproved of astrology, some physicians still used it. Medieval medicine therefore contained different influences rather than one universally accepted explanation.

The Four Humours: illness as an imbalance

The Theory of the Four Humours held that the body contained four fluids: blood, phlegm, black bile and yellow bile. Health depended on these humours being in balance. Too much or too little of a humour was believed to cause illness.

Imagine a balance that has tipped to one side. In this theory, the problem was not simply the presence of a fluid—all four belonged in the body—but an incorrect balance between them. The humours were also linked to seasons and other features of the natural world, helping people connect changes around them with changes in health.

Physicians tried to identify an imbalance by examining patients. One method was inspecting urine: they compared its colour, consistency and smell with a urine chart to judge which humour was unbalanced. Observation was therefore part of medieval medicine, but physicians interpreted what they saw through an incorrect theory.

Miasma: illness from bad air

Miasma theory explained disease through the environment rather than an imbalance inside the body. People believed that bad air, associated with swamps, corpses and rotting material, caused illness when breathed in.

The connection seemed plausible because decay produced unpleasant smells. However, a smell was not proof that the air itself caused disease. Belief in miasma explains why pleasant smells were thought to offer protection: people hoped to counteract the harmful air.

Why Galen remained influential in England

Galen was an ancient Roman physician who developed the Four Humours theory. His Theory of Opposites linked the explanation of illness to treatment: an excess of a humour should be counteracted with opposite qualities. For example, excess phlegm was associated with coldness, so a hot food such as pepper was thought to help. The distinction matters: imbalance explained the illness; opposites guided the response.

Galen also studied anatomy by dissecting animals, including pigs. Applying findings from animals to humans led to errors, yet his writings remained authoritative for many centuries.

Several factors reinforced his influence in medieval England. His ideas were considered compatible with Church teachings, so Church support helped preserve their authority. Educated physicians who had studied his writings were respected, while many patients could not read those works or challenge their interpretation. There were also no widely accepted, better explanations to replace his theories. Together, religious authority, respect for ancient learning and limited alternatives encouraged continuity in medical thinking.