Nature of Man

Summary

Nature of Man is a short Greek medical treatise from the Hippocratic Corpus, probably written around 400 BCE. It is the only surviving text from classical antiquity that sets out the four-humour theory in full: the body is composed of blood, phlegm, yellow bile, and black bile, each linked to a season and a pair of qualities. The text was a minority position when it was written — most Hippocratic authors worked with only two humours. But Galen, writing six centuries later, selected it as the authentic voice of Hippocrates and built his entire medical system on its framework. Through Galen, the four-humour scheme became the foundation of Western medicine for the next fifteen hundred years. The history of Nature of Man is a case study in how one marginal text, elevated by a later authority, can reshape an entire tradition.

Authorship and the Polybus Question

The Hippocratic Corpus was not written by one person. It was assembled in Alexandria in the third century BCE under the name of Hippocrates, but its fifty to seventy constituent texts were composed between roughly 480 and 380 BCE by multiple authors from different schools, and they contain mutually contradictory positions (Ackerknecht, 1955).

Nature of Man is among the texts whose authorship is most disputed. Aristotle attributed part of it to Polybus, identified in the tradition as Hippocrates’ son-in-law (Nutton, 2023). Nutton reports that later commentators (Sabinus in the first century CE, Galen in the second) rejected Aristotle’s attribution and insisted the treatise was genuinely Hippocratic, but the modern consensus follows Aristotle (Nutton, 2023). Whether the text is by Polybus, by Hippocrates, or by an anonymous Coan physician cannot be settled from the surviving evidence. What matters for the history of medicine is not who wrote it but what was done with it.

The Argument of the Text

Nature of Man opens with a polemic. Its author attacks the proposition that the body is composed of a single substance, the “monistic hypothesis,” which Longrigg associates with Diogenes of Apollonia and other Presocratic natural philosophers (Longrigg, 1998). The argument runs that if the body were composed of only one element, a person could never fall ill, because there would be nothing for that element to be overwhelmed by. Since people do fall ill, the body must be composed of multiple substances whose imbalance produces disease.

Having dismissed monism, the author proposes four constituent humours in the key passage of Nature of Man 4: “The human body has within itself blood and phlegm and yellow and black bile, and these are the nature of the body, and because of them it suffers and is healthy. So it is particularly healthy when these things maintain a balance of their power and their quantity in relation to one another, and when they are thoroughly mixed together. It suffers when one of them becomes either too small or too great, or is separated in the body and is not mixed with all the others.” (Pormann (ed.), 2018)

Blood, phlegm, yellow bile, and black bile. Health consists in the correct mixture of these four; disease arises from their improper blending. Stapley underlines the historical weight of this move: the naming of these four humours in Nature of Man set a pattern of belief that held sway for over a thousand years and is, for that reason, foundational to the narrative of British medicine. (Stapley, 2024) The therapeutic principle follows directly: “the physician must set himself against the established character of illness”; opposites cure opposites (Jouanna, 1999). A disease characterized by excess cold and moisture (phlegm) is treated with warming and drying interventions; one marked by excess heat and dryness (yellow bile) is treated with cooling and moistening.

The text then links the humours to the annual cycle. Jouanna summarizes: “phlegm, cold and moist, predominates in winter; blood, warm and moist, in spring; yellow bile, warm and dry, in summer; and black bile, cold and dry, in fall” (Jouanna, 1999). This seasonal correspondence gave physicians a temporal framework for prevention: the author prescribed vomiting in winter to clear phlegm from the upper body, and bowel evacuations in summer to cool the lower body’s accumulated bile (Jouanna, 1999). Preventive medicine was thus a matter of seasonal calibration.

The treatise also draws a distinction between diseases caused by regimen and those caused by the common air — a distinction that would matter greatly for epidemic medicine. Nature of Man 9 states: “Some diseases arise from regimen, others from the air we inhale … When many people are stricken with a single disease at the same time, we should assign as the cause of it whatever is the most common factor, the one which all of us make use of: this is what we inhale. For it is clear at any rate that it is not each individual’s regimen that is responsible, when the disease attacks everybody one after the other, both younger and older, women and men, wine-drinkers no less than those who drink water, those who eat barley cakes and those who consume bread, and those who exert themselves greatly and those who do not.” (Pormann (ed.), 2018) This passage anchors epidemic causation in shared environmental exposure rather than individual constitution.

The treatise also described what Jouanna calls “selective humoral evacuation”: medicines that withdraw phlegm cause phlegm-vomiting; those that withdraw bile cause bile-vomiting; those that withdraw black bile purge it; wounding causes blood to flow (Jouanna, 1999). This claim is striking because it treats the humours as genuinely separable substances, each responding to its own specific purgative. The pharmacological assumption (that different drugs selectively target different humours) would remain central to Western therapeutics for two millennia.

A Minority Position

The four-humour theory is so thoroughly identified with “Hippocratic medicine” that it takes an effort of historical imagination to recognize how marginal it was within the Corpus itself. Nutton states this directly: “The subsequent importance of this tract and its exposition of the theory of the four cardinal humours should not be allowed to disguise the fact that this was very much a minority view, even within the Corpus, and was, as we shall see, disputed by many later writers” (Nutton, 2023). The very framing of Nature of Man as an appeal to the “nature of man” reflects a broader fifth-century intellectual move: Lane Fox argues that Hippocratic authors excluded the gods from medicine by grounding health and disease in a naturalistic philosophy derived from the mid-sixth-century Presocratic revolution, yet they were not atheists but understood the craft as having its own momentum within divinely ordained regularities. (Lane Fox, 2020)

The Hippocratic Question itself sharpens this point. Craik’s analysis of the Corpus notes that the four-humour theory appears only sporadically across the collection and is not the foundational doctrine of the Corpus as a whole; it is systematically presented chiefly in Nature of Man.(Pormann (ed.), 2018) The text is nonetheless the most systematic Hippocratic formulation of the theory: blood, phlegm, yellow bile, and black bile are identified as the fundamental constituents of the body, each linked to a season, organ, and quality.(Pormann (ed.), 2018)

Most Hippocratic authors worked with two humours, not four. Nutton observes that “the two most important humours in the Hippocratic Corpus were phlegm and bile, visible and easily associated with illness” (Nutton, 2023). The author of Affections wrote flatly: “All human diseases arise from bile and phlegm” (Nutton, 2023). Blood was obvious but did not require a special theoretical status; black bile was new.

Nutton argues that “the concept of black bile as a separate humour was relatively new at the end of the fifth century” (Nutton, 2023). The author of Nature of Man himself referred to it as “the so-called black bile,” a formulation that implies the term was not yet universally familiar (Nutton, 2023). Nutton reads this as evidence that black bile was likely “hypostatized” (turned from a description of a type of bile into a distinct substance) in order to complete a cosmological scheme of fours (Nutton, 2023). The scheme demanded four humours to match Empedocles’ four cosmic elements (earth, air, fire, water), each linked to a pair of four primary qualities (hot, cold, wet, dry) (Nutton, 2023).

The Philosophical Irony

One feature of the text’s polemical stance is that it names its intellectual opponents, though only briefly. Among the Hippocratic Corpus, only two writers are mentioned critically by name in passing: Empedocles in Ancient Medicine and Melissos in Nature of Man. These allusions are fleeting and incidental — not sustained arguments but gestures of dismissal toward competing philosophical positions. (Pormann (ed.), 2018) The mention of Melissos, the Eleatic philosopher who argued for a single, unchanging substance underlying all apparent multiplicity, places Nature of Man’s anti-monism in direct dialogue with fifth-century Presocratic debate.

Longrigg identifies a deep irony in the text’s intellectual history. Nature of Man opens by attacking the intrusion of philosophy into medicine; it is explicitly hostile to the monistic hypotheses of the natural philosophers. And yet, as Longrigg puts it, the four-humour theory that it proposes as an empirically justified alternative “is, in fact, the medical counterpart of the Empedoclean theory of the four elements” (Longrigg, 1998). The very treatise that set out to free medicine from philosophical speculation ended up importing one of philosophy’s most influential structural ideas.

Longrigg draws the consequence: “It is highly ironical that a treatise so concerned to attack the intrusion of philosophy into medicine should itself not only reveal strong philosophical influence in this way but also, as a result of this influence, should formulate a theory which, more than any other, was to contribute to the dominance of philosophy over medicine for the next two millennia and beyond” (Longrigg, 1998). The four-humour theory became the vehicle through which a cosmological framework (the scheme of fours linking elements, qualities, seasons, and temperaments) colonized medical thinking for longer than any other single idea in the history of Western medicine.

At the same time, Longrigg insists that the relationship between philosophy and Hippocratic medicine was not simply one of intrusion. The sceptical, empirical attitude of Ancient Medicine, a different Hippocratic text that rejected the four-element framework, can itself be traced back to earlier Presocratic philosophical debate (Longrigg, 1998). Without its philosophical background, “Hippocratic medicine is inconceivable”: from philosophy, medicine derived its rational attitudes, its belief that human beings were products of their environment, subject to natural laws, with diseases running their courses independently of supernatural interference (Longrigg, 1998). The question was never whether medicine would be shaped by philosophy, but which philosophical framework would prevail.

Another Hippocratic Text Disagrees

The internal diversity of the Corpus is visible in the direct contradiction between Nature of Man and another major Hippocratic treatise, On Ancient Medicine. French observes that the author of Ancient Medicine rejected the four-element, four-quality framework as simplistic, arguing that “it is absurd … to explain medicine and indeed the whole world on the basis of the four elementary qualities, the Hot, Cold, Dry and Wet” (French, 2003). For that author, the many subtle qualities of foods (bitter, salt, acid) were the true causal agents in health. The body was too complex for a fourfold scheme.

This disagreement was not a marginal scholarly dispute. It was a fundamental conflict about what kind of knowledge medicine should be. Nature of Man moved toward abstraction and cosmological symmetry, while Ancient Medicine moved toward empirical observation and resistance to system-building. Nutton’s summary of the broader situation captures what was at stake: “The diversity of standpoints found in the medical writings of the late fifth and early fourth centuries is arguably greater than that in any other comparable block of Classical Greek literature” (Nutton, 2023). The four-humour theory won its eventual dominance not because it settled this debate within the Corpus but because a later authority, Galen, chose it.

Galen’s Reconstruction

Six centuries after the Corpus was assembled, Galen reconstructed Hippocrates in his own image. French’s analysis is direct: Galen made Hippocrates into a Rationalist, a great anatomist, and the originator of the four-element theory, “thereby giving ancient authority to Galen’s own philosophical medicine” (French, 2003). Nature of Man was the text through which Galen accomplished this reconstruction. The Corpus contained dozens of competing positions, but Galen selected the four-humour doctrine as the authentic core of Hippocratic thought and dismissed the rest as the work of students or later interpolators.

Temkin summarizes the result: “Galen’s interpretation defined Hippocratic medicine as the great patristic authors were to see it. Its main points were the basic roles of the four ‘classical’ humors, and an allopathic principle of therapy … Contraria contrariis curantur” (Temkin, 1991). Through Galen, the four-humour theory became not merely one Hippocratic position among many but the Hippocratic position, the lens through which all subsequent readers would approach the Corpus.

Galen went further. He declared the first aphorism of the Aphorisms to be evidence that Hippocrates was a Rationalist, interpreting the “deceptive experience” as “Empiricist business” and the “difficult judgement” as “a Rationalist affair” (French, 2003). His commentary concluded “with the unambiguous statement that Hippocrates, in all the aphorisms, was a Rationalist” (French, 2003). This was not simply a reading of the text. It was a claim about what medicine fundamentally was. And the text that anchored the claim was Nature of Man.

Galen built a medical system on this foundation. He accepted nine possible temperaments based on the four primary qualities, with every individual possessing a natural mixture that the physician sought to restore through therapy (Nutton, 2023). The four humours, the four elements, the four qualities, and the seasonal correspondences from Nature of Man became the structural supports of the most influential medical system in Western history.

The Medieval Reception

The Alexandrian medical school established a canon of sixteen Galenic writings for reading and commentary, and the framework derived from Nature of Man via Galen was central to it (Temkin, 1973). When this material passed into Arabic through the translation movement and then into Latin through figures like Gerard of Cremona and Constantine the African, the four-humour scheme travelled with it (Rawcliffe, 1997).

Medieval Galenism, however, was not Galen as he wrote. Temkin observes that “medieval Galenism was not just Galen as read and accepted by medieval readers; it was a medical philosophy twice removed from him, viz., through the activities of Byzantines and Arabs” (Temkin, 1973). The Ars Medica by Galen and the Isagoge of Iohannicius became the two central texts of the Articella, the core curriculum of medieval medical education (Temkin, 1973). Both transmitted the framework of Nature of Man at yet another remove: systematized, schematized, and simplified.

The scheme arrived in late medieval England intact. Rawcliffe documents that the Articella, or Ars Medicinae, comprising selected works by Galen and Hippocrates, provided the basis of the university syllabus, supplemented by Avicenna’s Canon and by Averroes and Rhazes; the student learned from Avicenna that “the immutable principles of philosophy” could never be disproved by fallible human experience. (Rawcliffe, 1997) Rawcliffe describes how the four humours (choler or yellow bile, phlegm, black bile, and blood), each corresponding to one of the four elements and their qualities: fire (hot and dry), water (cold and wet), earth (cold and dry), and air (hot and wet) (Rawcliffe, 1997). This framework was not confined to university physicians. Rawcliffe observes that Galenic humoral theory “remained the dominant framework for understanding health and disease in late medieval England at all social levels, with laymen sharing the same vocabulary as university-trained physicians” (Rawcliffe, 1997).

Elliott, writing in 1914, summarized the system as later tradition received it: “health depended on the proper proportion and action in the body of the four elements, earth, water, air, and fire, and the four cardinal humours, blood, phlegm, yellow bile and black bile. The due combination of these was known as crasis” (James Sands Elliott, 1914). This is recognizably the scheme of Nature of Man, transmitted through Galen and the Arabic-Latin tradition, arriving in a twentieth-century medical history textbook as established fact. By this point, the text’s original marginality within the Corpus had been completely effaced.

The Healing Power of Nature

Nature of Man also contributed to one of the most persistent ideas in Western medicine: that disease itself contains the mechanism of recovery. Neuburger reads the Hippocratic tradition as establishing that “the disease appears not purely as pathos, as a malady, but also, and in no way in the last line, as ponos, that is, as a work, an effort of the body to reestablish the disturbed equilibrium” (Neuburger, 1943). The aphorism nousoon physies ietroi (“nature is the healer of disease”) encapsulated this principle.

The connection to Nature of Man is structural. If health is the correct mixture of humours, and disease is their imbalance, then the body’s spontaneous tendency to restore balance is the healing process. The physician’s role, on this view, is not to impose health from outside but to support the body’s own restorative work, primarily through regimen, and through drugs or surgery only when the body’s own efforts fail or go astray. The therapeutic hierarchy of diet, drugs, and surgery that governed Western medicine for two millennia rests, at bottom, on the humoral physiology that Nature of Man articulated.

See Also

• Hippocratic Corpus
• Humoral Theory
• Galen
• Polybus
• Empedocles
• Regimen
• Dietetics
• On Airs Waters Places
• Sacred Disease
• Vis Medicatrix Naturae

Sources

Primary evidence for this page comes from:

• Nutton, V. (2023). Ancient Medicine (3rd ed.). London: Routledge. [Source ID: nutton-ancient-medicine-2023]
• Jouanna, J. (1999). Hippocrates. Trans. M. B. DeBevoise. Baltimore: Johns Hopkins University Press. [Source ID: jouanna-hippocrates-1999]
• Longrigg, J. (1998). Greek Medicine from the Heroic to the Hellenistic Age. London: Duckworth. [Source ID: longrigg-greek-medicine-heroic-1998]
• Lane Fox, R. (2020). The Invention of Medicine. London: Allen Lane. [Source ID: lane-fox-invention-medicine-2020]
• French, R. (2003). Medicine Before Science. Cambridge: Cambridge University Press. [Source ID: french-medicinebefore-2003]
• Temkin, O. (1991). Hippocrates in a World of Pagans and Christians. Baltimore: Johns Hopkins University Press. [Source ID: temkin-hippocratespagans-1991]
• Temkin, O. (1973). Galenism: Rise and Decline of a Medical Philosophy. Ithaca: Cornell University Press. [Source ID: temkin-galenism-1973]
• Ackerknecht, E. H. (1955). A Short History of Medicine. New York: Ronald Press. [Source ID: ackerknecht-shorthistory-1955]
• Elliott, J. S. (1914). Outlines of Greek and Roman Medicine. London: Bale, Sons and Danielsson. [Source ID: elliott-outlines-greek-roman-medicine-1914]
• Rawcliffe, C. (1997). Medicine and Society in Later Medieval England. Stroud: Sutton. [Source ID: rawcliffe-medievalengland-1997]
• Neuburger, M. (1943). The Doctrine of the Healing Power of Nature. Trans. L. J. Boyd. New York. [Source ID: neuburger-healing-power-of-1943]

Editorial Notes

Gaps the encyclopaedia compiler flagged for future evidence work, collected from inline markers in the body and frontmatter.

The Healing Power of Nature