Humoral theory and the four qualities

What it is

The framework that organised medicine across most of the literate world for most of recorded history: that health is a balance of a small number of bodily principles, and that substances act by shifting that balance along axes of temperature and moisture.

The Greek version, systematised by Galen from Hippocratic material, has four humours — blood, phlegm, yellow bile, black bile — each pairing two of four qualities: hot, cold, wet, dry. Blood is hot and wet, phlegm cold and wet, yellow bile hot and dry, black bile cold and dry. Health is their balance; disease is an excess or deficiency; and treatment corrects it with a substance of the opposite quality.

Galen graded every medicinal plant by degree — first through fourth — of heat or cold. Pepper is hot in the third degree. That is a quantified pharmacology, three centuries before anyone could measure anything.

Where it came from

Independently, several times, which is the interesting part.

• Greece, from the Hippocratic corpus through Galen, and thence to all of Europe and the Islamic world.
• India, in Ayurveda's three doṣas — vāta (mobile, dry, cold), pitta (hot, sharp, oily), kapha (heavy, cold, damp) — with vīrya grading substances as heating or cooling.
• China, in the four natures of the bencao tradition: hot, warm, cool, cold, alongside five flavours and a yin-yang framework built on complementary opposites.
• The Islamic world, in Unani, which took the Greek system and refined it — and whose name simply means "Greek".

Similar schemes appear in Tibetan medicine, in Latin American humoral folk medicine, and in the hot–cold food classifications still used domestically across much of Asia and the Mediterranean by people with no interest in medical theory at all.

How it is used

To classify substances and to match them to conditions. It is also, in every one of these systems, the bridge between medicine and diet — which is why "warming" and "cooling" foods are a live category in kitchens from Guangzhou to Naples.

What we can and cannot say

We can say the convergence is real and requires an explanation. Four unconnected literate traditions arrived at temperature-and-moisture as the organising axes of medicine. That is not coincidence and it is not diffusion in most of these cases.

We can offer the two explanations on the table, and this is where the article earns its place.

The perennialist reading: they converged because they were all describing something real about how bodies and substances work.

The constructivist reading, which is the stronger one here: they converged because they were all human beings with the same equipment. Fever and chill are the most salient sensations of being ill. Wet and dry describe the discharges and dessications a sick body actually produces. Chilli genuinely produces a burning sensation; mint genuinely produces a cooling one, because menthol activates the cold receptor TRPM8. Anyone anywhere, reasoning carefully from the available evidence and lacking a microscope, would build something like this.

The convergence is a fact about the observers, not about the world — the same argument set out under perennialism and constructivism. It does not follow that the systems are worthless; it follows that agreement between them is not the independent confirmation it looks like.

We can say it was refuted, and how. Rudolf Virchow's cellular pathology in 1858, germ theory, and the chemical isolation of active compounds ended humoral medicine as a scientific framework. Nothing corresponds to black bile. The theory also licensed centuries of bloodletting, which killed an unknown but substantial number of people — the treatment follows directly from the theory, and that is the clearest available demonstration that a coherent, long-lived, universally accepted framework can be entirely wrong.

And we can say the vocabulary outlived the theory everywhere. Western herbalists still speak of warming and cooling herbs. Chinese and Ayurvedic practice retains the categories as living doctrine. Ordinary people describe foods as heating without knowing where the idea came from. The words are Galen's, four hundred generations downstream, in kitchens whose owners have never heard of him.

We cannot say the qualities track anything physiological. What can be said is that they track something perceptual reliably enough that four civilisations built medicine on them, and that this is a more interesting fact about people than about plants.

Further reading

• Vivian Nutton, Ancient Medicine (2004).
• Noga Arikha, Passions and Tempers: A History of the Humours (2007).
• Shigehisa Kuriyama, The Expressiveness of the Body (1999) — compares Greek and Chinese medicine on exactly this question, and is one of the best books in the field.