The Four Humors

The Four Humors were four bodily fluids—blood, yellow bile, black bile, and phlegm—that ancient physicians believed determined a person's temperament and health, with imbalances leading to illness[1][3]. This medical theory persisted for more than 2,000 years in the West until the rise of controlled empirical science in the mid-19th century[3].

Origins and Development

The origins of the Four Humors can be traced back to ancient Egypt and Mesopotamia, although it is often attributed to the Greek physician Hippocrates of Kos[4]. In the mid-5th century BCE, the philosopher Empedocles devised a theory that divided human life into four elements: fire, water, air, and earth[8]. Hippocrates and his followers developed these ideas further, suggesting that the balance of the humors was essential for health[4].

One of the Hippocratic texts Galen believed to be most important was On the Nature of Man, which articulates the famous humoral theory of the body and offers a coherent presentation of the four humors: blood, phlegm, yellow bile, and black bile[12]. The Hippocratics were the first organized group to consider that illness had natural—not supernatural—causes[3], representing a revolutionary shift in medical thinking.

Galen's Contributions

The Greek physician Galen of Pergamum (AD 129–c.216) was the first major systematizer of medical practice and theory in the ancient world, with his work based on the ideas of Hippocrates as well as Platonic, Aristotelian, and Stoic philosophy[11]. Galen, a prominent Roman physician, elaborated on how different lifestyles, diets, and environments could affect the humors[4].

Building on earlier Hippocratic conceptions, Galen believed that human health requires an equilibrium between the four main bodily fluids, with each of the humours built up from the four elements and displaying two of the four primary qualities: hot, cold, wet, and dry[18]. Unlike Hippocrates, Galen argued that humoral imbalances can be located in specific organs, as well as in the body as a whole, allowing doctors to make more precise diagnoses and to prescribe specific remedies to restore the body's balance[18].

The Four Humors and Their Properties

### Blood Blood makes the body hot and wet[6]. A person whose temperament is based on blood is filled with energy, resulting in a sanguine personality[6]. Blood was associated with a sanguine temperament, characterized by a lively and social nature[4].

### Phlegm Phlegm, a fluid that made up the colorless secretions of the body results in a cold and wet body and serves as a lubricant and coolant[6]. Phlegm was linked to a phlegmatic temperament, often seen as calm and quiet[4]. A phlegmatic or passive, calm temperament is associated with an excess of phlegm[6].

### Yellow Bile Choler or yellow bile was gastric juice that serves digestion and makes the body hot and dry[6]. Yellow bile corresponds to a choleric temperament, which can be passionate and irritable[4]. Someone with a yellow bile temperament is bilious and choleric, showing a predilection toward anger[6].

### Black Bile Black bile or melancholy, was a dark liquid almost never found in pure form that caused other fluids to darken such as when the blood, skin, or stools become black, and it produced a cold and dry body[6]. Black bile was tied to a melancholic temperament, typically reflective and reserved[4]. A melancholic temperament comes from an abundance of black bile resulting in a predilection toward introspection and sentimentality[6].

Theoretical Framework

In its tidy arrangement of the naturally balanced humours, the body was a microcosm of the universe at large, whose equilibrium depended on four elements – earth, air, fire, and water[2]. These, like the humours, were located at the intersections of two criss-crossing qualitative axes: warm and cool, wet and dry, with echoes observable in the Mediterranean seasons – spring (hot and wet), summer (hot and dry), autumn (cold and moist), and winter (cold and dry) – and the stages of life of man, the temperaments of man (phlegmatic, sanguine, choleric, melancholic)[2].

Each humor was associated with one of the four seasons, and each was considered to have characteristic qualities of hotness, coldness, dryness, and wetness, with each individual's humoral balance holistically connected with other phenomena—such as climate, diet, occupation, geographic location, planetary alignment, sex, age, and social class[5].

Medical Practice and Treatment

In humoral theory, individual diseases did not exist in the way that we understand them today, as diseases were not seen as forces or entities separate from the body, but instead were understood as states of bodily imbalance[5]. The physician's task was to diagnose which humor was out of balance; treatment then focused on restoring equilibrium by diet or by reducing the offending, out-of-balance humor by evacuating it[3].

Bloodletting as a treatment was closely associated with humoral theory, as in cases of an overabundance of one or another humor, letting blood was believed to allow the body to reach a healthier balance[5]. Medical practices involved various interventions aimed at restoring balance, such as bloodletting, dietary changes, and physical remedies[4].

Physicians trained in humoral theory relied not only on a knowledge of medical texts, but also on personal understanding of the patient; on the inspection of blood, urine, and other fluids produced by the body; and on the patient's description of his or her symptoms, with extensive physical examinations being rare[5].

Historical Transmission and Influence

After the fall of the Roman empire in the fifth century AD, Galen's writings were preserved by Arab scholars and retranslated into Latin in the eleventh century, with Galenic works serving as the basis for university medical study until the discoveries of the Italian anatomist Vesalius (1514–1564) in 1543[11].

Greek manuscripts began to be collected and translated by enlightened Arabs in the 9th century, and about 850 Ḥunayn ibn Isḥāq, an Arab physician at the court of Baghdad, prepared an annotated list of 129 works of Galen that he and his followers had translated from Greek into Arabic or Syriac, making learned medicine in the Arabic world heavily based upon the commentary, exposition, and understanding of Galen[18].

Galen's influence was initially almost negligible in western Europe except for drug recipes, but from the late 11th century Ḥunayn's translations, commentaries on them by Arab physicians, and sometimes the original Greek writings themselves were translated into Latin, forming the basis of medical education in the new medieval universities[18].

Cultural Impact

The theory of the four humors underpinned European medicine and thinking on the innerworkings of the body until at least the 1700s[1]. These naturally occurring personalities appeared in thousands of ways in ancient, medieval, and early modern periods, especially within art, from characters within Chaucer's Canterbury Tales to Shakespeare's Taming of the Shrew, with artists throughout history taking inspiration from Hippocratic medicine to create some of their most convincing protagonists, antagonists, and everything in between[8].

The theory of the four humours in ancient, medieval, and early modern minds underpinned understanding of the human body's interaction with the environment and defined for centuries the way in which disease and illness were thought to work, how emotions fluctuated, and the impacts of age and sex on health[9].

Decline and Legacy

Though several important publications—Andreas Vesalius's De Humani Corporis Fabrica in 1543 and William Harvey's De Motu Cordis in 1628—challenged aspects of humoral theory, it remained dominant among both physicians and the public through the 19th century[5]. After the first decades of the 19th century, bloodletting was discredited in many parts of Europe and the United States, though the practice continued well past mid–century[5].

In the late 1700s, Joseph Priestley and Antoine Lavoisier discovered modern chemical elements and blew up Aristotle's four-part explanation of what makes up the world, and by the late 1800s, germ theory offered a decisive new paradigm for understanding disease[2]. The 19th-century theory of germs and bacteria as a cause for the spread of diseases made Hippocratic medicine obsolete[8].

Although the theory of the four humors is now obsolete, it was a crucial step in the history of medicine, providing a framework for understanding the human body and disease that influenced medical practice for centuries, with many of the terms and concepts associated with the humors, such as "sanguine" or "melancholic," remaining in use today in a more metaphorical sense to describe personality traits[19].

Medical traditions in other cultures, such as Ayurvedic medicine in India, traditional Chinese medicine, and Native American medicine, are also based in versions of humoral theory[5], demonstrating the enduring influence of this ancient medical framework across different civilizations.