THE SIGNIFICANCE OF
THE THEORY OF THE FOUR HUMOURS
for Medieval Medicine

The foundation of Hippocratic and Galenic methods and treatments was the Theory of the Four Humours. 

To understand the Theory of the Four Humours you need to understand the Greek philosophers. 

They wanted to understand ‘how the world works’, but they did not have any of our technology or science … so they looked, and they thought, and they tried to build what they saw into an encompassing model. 

You can see them building the Theory of the Four Humours over time.  It started with a 6th century BC philosopher called Anaximander, who postulated that matter was made of four ‘elements’ – water, fire, earth and air.  Water was wet and cold; earth cold but dry; fire dry and hot; and air (if one stretched things a little) hot and wet.  From there it was a small step to link all that to the seasons: winter was wet and cold; summer was dry and hot; and (if you stretched things a little) could one not say that Spring was hot and wet, and that autumn was cold and dry? 

So it was inevitable that this model would eventually turn up as a theory for health.  The body was clearly matter, comprised of the four elements, and it clearly got hot, cold, wet and dry … so it made sense when Greek doctors suggested that the body was made up of four fluids (‘humours’).  Two were easy – blood is clearly warm and wet, and phlegm is just as obviously cold and wet.  To complete the model, the Greeks shoehorned in two other humours, which they said were produced in the liver during digestion – ‘yellow bile’ (which really exists, and can turn your poo yellow) and ‘black bile’ (which they said was collected in the spleen). 

Nobody knows today what this ‘black bile’ was, but generations of doctors knew what they were looking for, and Galen wrote a book on how to recognise it: it turned parts of the body and excreta black, it was thick and sticky, cold and dry, heavy and earth-like – like the sediment at the bottom of a glass of wine.  One modern suggestion is that it was blood clots – vomiting black bile after a wound in battle was a sign you were going to die. 

Therefore, declares the Greek text On the Constitution of Man:

Man's body has blood, phlegm, yellow bile and black bile.  These make up his parts and through them he feels illness or enjoys health.  When all these humours are truly balanced and mingled, he feels the most perfect health.  Illness occurs when one of these humours is in excess, or is lessened in amount, or is entirely thrown out of the body. 

And that explains illness at a common-sense level. 

In winter, when you got cold and wet, you might catch a cold or flu, and your sneezing and runny nose would be a sign that you had too much phlegm in your body.  In summer, if you got too hot and dry, you might suffer from dehydration and sunstroke, and vomiting might be a sign that you had too much yellow bile in your system.  We know now that these are the symptoms of the malady, but it is easy to see why physicians thought they were the cause. 

How might one stay healthy? 

The Theory of the Four Humours defined the healthy lifestyle – in winter keep your warmth balanced by eating lots of rich food, drinking full-bodied wine and taking exercise; in summer eat light and stay cool. 

If you were ill, the Theory could supply a cure. 

If you had a fever, most doctors would peremptorily declare that you were too hot because you had too much blood, and prescribe phlebotomy (bleeding) to get rid of some.  Doctors would advise vinegar & honey, or a bowl of warm barley soup to bring up phlegm.  We still say: “feed a cold and starve a fever”. 

Mental health, also, was linked to the four humours. 

The Greeks believed that the humours affected personality.  The Latin word for ‘blood’ is ‘sanguis’, which gives us our word ‘sanguine’, meaning hopeful/optimistic.  ‘Melancholy’ means, literally, ‘black bile’.  A ‘phlegmatic’ person is easy-going.  The word ‘choleric’ means bad-tempered nowadays, but originally meant ‘bilious’ – ill from yellow bile; the word ‘bile’ is still used in the sense of ‘spite’.  And we still say that someone is ‘ill-humoured’ or ‘good-humoured’. 

Medieval universities based their medical curricula on the Four Humours;

... students learned how to recognise and balance the humours long before they ever saw a patient.  The Church picked up on the idea too, for instance linking melancholy to sloth or despair – sinful states requiring treatment and spiritual help. 

Finally, because the Four Humours theory was SO respected,

...  it fostered the idea that ancient knowledge was superior and unchallengeable, even when it didn’t work.  This hindered innovation and medical progress, because even questioning doctors such as de Mondeville were reluctant/unable to challenge humoral explanations. 

Thus, we can see that the Theory of the Four Humours had a MASSIVE significance in the Middle Ages, with echoes lasting right through to today:

1.  It was the foundation of medieval physiology, their understanding of how the body worked. 

2.  It was the basis of their diagnosis of a patient’s illness. 

3.  It advised their everyday health regimes. 

4.  It determined the treatments they prescribed. 

5.  It dominated university teaching – and even influenced some of the Church’s teaching. 

6.  It was used to explain people’s differing temperaments, and was the basis of mental health. 

7.  It was SO influential that it took medicine down a two-millennia-long wrong turning which actually stopped doctors from trying to find the correct causes of disease. 

8.  It still continues to influence homespun treatments and the language we use today.