Six Non-Naturals

Summary

The six non-naturals were the central framework of Galenic preventive medicine: the six categories of external influence — air, food and drink, sleep and waking, movement and rest, retention and evacuation, and the passions of the soul — that a person could, in principle, control. Unlike the body’s innate constitution or the course of a disease already underway, these factors were modifiable. Keeping them in balance, tailored to one’s individual temperament, was the physician’s primary tool for maintaining health. The label “non-naturals” (Latin: res non naturales) distinguished them from the body’s inherent structures (“naturals”) and from frank disease (“contra-naturals”). Though the ideas behind the categories are ancient, the tidy list of six was not Galen’s own formulation. It was assembled by medieval scholars from scattered Galenic passages, codified in ninth-century Arabic summaries, and taught in Western universities until well into the eighteenth century.

The Six Categories

Pormann and Savage-Smith give a clean enumeration of the six: “surrounding air, food and drink, sleeping and waking, exercise and rest, retention and evacuation (including bathing and coitus), and mental states (anger, sadness, joy, love, and so forth).”(Pormann, 2007)

Each category organized a distinct domain of lifestyle management.

Air covered not just the immediate atmosphere but the broader environment: climate, season, topography, and the condition of local water and soil. This was the Hippocratic inheritance — the treatise Airs, Waters, and Places gave physicians a vocabulary for analyzing how places made people sick or well. In plague medicine, it became the theoretical engine behind fumigation, bonfires, and street-cleaning campaigns.(Wear, 2000)

Food and drink was the most elaborated category because, within Galenic physiology, food was the origin of all three systems of bodily function: it became venous blood (liver and nutrition), vital arterial blood (heart and life), and animal spirits (brain and sensation).(Wear, 2000) Because every food had a temperamental quality — hot or cold, moist or dry — diet was not merely about calories but about continuously correcting or worsening one’s humoral balance. Avicenna made explicit what the logic implied: food and medicine were formally distinct (food is assimilated by the body; medicine assimilates the body to itself) but practically continuous, since both operated on complexion through the same qualitative mechanism.(Siraisi, 1990)

Sleep and waking determined the rhythm of concoction and restoration. Sleep was when the body completed digestion; excessive sleep or waking at the wrong times disturbed the balance of innate heat and moisture.

Movement and rest was particularly important for the humoral economy because exercise generated heat, promoted digestion, and expelled superfluities through the skin and lungs. The sedentary scholar or gentleman — the target audience for most English regimen literature — was presumed to be at special risk from insufficient movement.(Wear, 2000)

Retention and evacuation covered the full range of excretory processes: bowel function, urination, sweating, menstruation, and sexual discharge. The category also encompassed therapeutic evacuations — bloodletting, purging, emetics — which were the principal tools of active Galenic treatment as well as of preventive maintenance.(Siraisi, 1990) The boundary between preventive regimen and active treatment was porous at this point.

The passions of the soul — anger, fear, grief, joy, desire — were given a physiological account. Strong emotions altered the distribution of blood and spirits, moving heat toward or away from the vital centers. Al-Razi’s On Spiritual Medicine treated the governance of mental states as both a philosophical imperative and a bodily health measure, directly linking moral philosophy to Galenic hygiene.(Pormann, 2007)

Origins: Galen to Hunayn

Galen never wrote a treatise called “the six non-naturals.” He left extensive remarks about the factors that disturb health, scattered across his discussions of hygiene, pathology, and pulse theory — but he never assembled them into a canonical six-item list. What the tradition extracted from those scattered passages was nonetheless coherent as a program: regulating air, food and drink, movement and rest, sleep and waking, retention and evacuation, and the passions defined the physician’s primary task.(Dols, Michael W. (trans.), 1984)

Vivian Nutton, in his synthesis of late antique medicine, reconstructs how the list was made: a brief comment in Galen about the factors that alter the pulse was combined with a passage from his commentary on Hippocrates listing the determinants of health (diet, environment, exertion, sleep, excretions, and mental activity) to produce what later Galenists treated as a “programmatic statement of the aims of the whole art of medicine.” The technical term “non-naturals” itself was produced by the same act of conflation — fusing several separate Galenic passages into a phrase Galen never used.(Nutton, 2023)

This textual construction is characteristic of how Galenism worked as a tradition. The late antique encyclopaedists — Oribasius, Aetius of Amida, Paul of Aegina — assembled Galenic writings into systematic compilations, progressively reducing alternatives and attributing all content to Galen.(Nutton, 2023) By the time the Alexandrian curriculum stabilized around 500 CE into a canon of Galenic texts, the interpretive pressure to find system and completeness in those texts was intense.(Nutton, 2023)

The codification of the six as a list was accomplished by Hunayn ibn Ishaq (Latinized as Johannitius) in the ninth century. His Isagoge — an Arabic introduction to the Alexandrian Galenic syllabus — became one of the two foundational texts of the medieval Western medical curriculum alongside Galen’s Ars Medica.(Temkin, 1973) The Isagoge gave the six non-naturals a fixed schematic form, even while it also departed from Galen in other ways — most notably by flatly asserting three spirits (natural, vital, psychic) where Galen had been cautious or openly skeptical.(Temkin, 1973) The medieval list was thus not a recovery of authentic Galenism but a simplification that made transmission manageable.

Medieval and Islamic Elaboration

Once codified, the framework became a standard organizing principle for Islamic medical theory. Pormann and Savage-Smith describe it as a central feature of the humoral system: health could “often be regained by adjustment of the ‘six non-naturals’ — factors external to the body over which a person could have some control.”(Pormann, 2007) The emphasis on control was not incidental. Unlike the fixed facts of one’s constitution or the onset of an acute disease, the non-naturals were the domain of physician and patient agency.

Ibn Ridwan, the eleventh-century Egyptian physician whose commentary on Galen’s Ars Medica Dols translates and analyzes, gives the list its most direct statement: the six non-naturals are the inescapable causes of health and illness, producing health when managed well and illness when mismanaged.(Dols, Michael W. (trans.), 1984) His application of the framework to Egyptian conditions is unusually concrete. Writing about the first non-natural in local terms, he characterizes Egyptian food as inherently weak and quick to spoil — wheat bread inedible within a day and night, crops swift to change, even imported foodstuffs rapidly having their temperament altered to conform with the local environment.(Dols, Michael W. (trans.), 1984) The general doctrine here meets a specific geography.

Islamic elaboration extended the passions of the soul into explicit moral medicine. Al-Razi’s On Spiritual Medicine argued that the avoidance of “afflictions of the soul” — desire, regret, fear — was simultaneously a philosophical obligation and a path to bodily health.(Pormann, 2007) This integration of ethics and physiology was a live intellectual possibility within the Islamic Galenic tradition, not merely a pious addition.

In the Latin West, the non-naturals entered through the Articella — the collection of texts used to teach medicine at Salerno and subsequently at the European universities. Temkin observes that the Ars Medica passage listing the six was treated as providing the conceptual structure for the entire discipline of hygiene: “Down to the early nineteenth century hygiene was taught more or less under the headings of these six ‘non-naturals,’ as the medieval Galenists called them.”(Temkin, 1973)

Siraisi’s analysis of medieval university medicine emphasizes how the framework shaped the physician’s preventive role. Medical care, at least in theory, “consisted as much in a preventive health regime as in the treatment of disease.” The physician was supposed to tailor the patient’s non-naturals — diet, exercise, rest, environment, psychological state — to maintain the optimum complexion for that individual.(Siraisi, 1990) This was the formal ideal; Siraisi is also careful to note that medieval medicine had no means to alter the course of acute or serious chronic disease, and its genuine utility lay in naming illness within a coherent framework, prognostic skill, and the selection of treatments that were “simultaneously justifiable in terms of medical theory and usually innocuous.”(Siraisi, 1990)

Early Modern Persistence

Andrew Wear’s detailed study of English medicine between 1550 and 1680 shows the six non-naturals not as a declining relic but as the active organizational principle of an entire genre of health literature. Preventive medicine and regimen writing were “usually organised according to the ‘six non-naturals’, which some time after Galen came to provide the canonical categories around which advice on the preservation of health was based.”(Wear, 2000)

The English regimen books — Elyot’s Castel of Helthe, Cogan’s Haven of Health, Venner’s Via Recta ad Vitam Longam, and many others — were directed at the literate and prosperous. Wear characterizes this as “the luxury end of medicine”: the poor had little control over diet, air, exercise, or rest, so the framework naturally addressed those with sufficient means to make choices.(Wear, 2000) This was not hypocrisy but the logic of the doctrine itself: the non-naturals were the modifiable factors, and modifiability required resources.

The authors of these works knew perfectly well that their advice was rarely followed. Thomas Cogan quoted the common saying that “He that liveth by Physicke, liveth miserably,” and attributed non-compliance to the difficulty of self-discipline.(Wear, 2000) The admission was structurally built into the genre: the gap between regimen as written ideal and regimen as lived practice was acknowledged from the start.

The framework extended into domains beyond private lifestyle advice. Learned surgical writers — Ambroise Paré prominent among them — incorporated the full Galenic apparatus into their surgical treatises, including the six non-naturals, in order to give surgeons the rational “indications” that distinguished learned practice from empirical rule-of-thumb.(Wear, 2000) In plague medicine, the same categories organized both individual preventive advice and community-wide public health measures: plague tracts routinely addressed what individuals should eat, drink, and do to fortify themselves, alongside civic recommendations for purging corrupt air through bonfires and street-cleaning.(Wear, 2000)

The intersection of the non-naturals with moral theology was especially visible in the treatment of food and drink. Regimen literature “consistently moralised intemperance in eating and drinking as simultaneously a medical and a religious failing,” drawing on classical moderation ideals and scriptural texts, so that health advice and practical divinity reinforced one another.(Wear, 2000) “Temperance” carried both meanings at once — humoral balance and Christian restraint — and writers moved between them without apparent strain.

What is striking in Wear’s account is the stability of the framework. Across the sixteenth and seventeenth centuries, English regimen literature showed “a great deal of consensus about health advice, with no controversies or significant new arguments” — what Wear calls, following the Annales school, an example of l’histoire immobile. The only significant disruption came from Helmontian attacks on the whole enterprise of health advice, which rejected the Galenic framework root and branch.(Wear, 2000)

Decline and Legacy

The six non-naturals did not fall suddenly. Friedrich Hoffmann’s early eighteenth-century mechanistic medicine preserved the doctrine by reinterpreting it in corpuscular terms: temperament survived as a description of the mixture of blood particles, and the non-naturals survived as the factors that disturbed that mixture. Temkin notes that Hoffmann could still write, citing Galen, that “the habits of the mind follow the temperament of the body” — using Galenic language to clothe what was now a mechanical physiology.(Temkin, 1973)

What ended Galenic hygiene as a system was not a single refutation but the collapse of the theoretical foundations that gave the non-naturals their explanatory power. The “mechanization of qualities” — the transformation of hot, cold, moist, and dry from objective physical realities into subjective sensations — was, as Temkin notes, “as destructive to Galenic science as doing away with fire, air, water, and earth as chemical elements.”(Temkin, 1973) Once the primary qualities became secondary (merely felt, not real), the mechanism by which food, air, exercise, and emotion acted on the body’s complexion had no foundation.

Yet Galenic practice outlasted Galenic science. Dietetics, advice about sleep, exercise, and emotional management, and the general principle that lifestyle factors determine health continued to be prescribed throughout the eighteenth century because “Galenic dietetics and therapy had been practiced for hundreds of years and supposedly had prevented and cured diseases. There was no reason for thinking that they had stopped doing so.”(Temkin, 1973)

The survival into modern culture is not merely historical curiosity. Nutton cites mid-twentieth-century London studies showing “a continued belief in the six non-naturals as the prime determinants of health” among ordinary people — that is, lay explanatory frameworks for health and illness continue to map, with remarkable fidelity, onto the same six categories that organized Galenic preventive medicine.(Nutton, 2023) Contemporary health promotion — exercise, diet, sleep hygiene, stress management, air quality, bowel health — reproduces the ancient list without acknowledging it.

Sources

Nutton, Vivian. Ancient Medicine. 3rd ed. Routledge, 2023. Chapters 19–20.
Temkin, Owsei. Galenism: Rise and Decline of a Medical Philosophy. Cornell University Press, 1973. Chapters 1, 3, and 4b.
Pormann, Peter E., and Emilie Savage-Smith. Medieval Islamic Medicine. Edinburgh University Press, 2007. Chapter 3.
Siraisi, Nancy G. Medieval and Early Renaissance Medicine. University of Chicago Press, 1990. Chapters 4–5.
Wear, Andrew. Knowledge and Practice in English Medicine, 1550–1680. Cambridge University Press, 2000. Chapters 4, 5, and 7.
Dols, Michael W. Majnun: The Madman in Medieval Islamic Society. Oxford University Press, 1984. Chapters 2 and 7.

Summary

The Six Categories

Origins: Galen to Hunayn

Medieval and Islamic Elaboration

Early Modern Persistence

Decline and Legacy

See Also

Sources

Sources