Aristotelian influence in the formation of medical theory

 

 

Aristotelian influence in the formation of medical theory

Mythologic cradle of Greek medical thought

Early Greek medicine contained both natural and supernatural elements. Pharmaka, a

broad term for drugs, referred to applications for magic, for poison, and for curing. The

gods had a large role. The Iliad opened with an epidemic sent by Apollo, and medical

solutions were often a search to discover what offended a particular god. By the time of

Hesiod (~700 B.C.), Asclepian healing ceremonies consisted of a normalized set of

rituals involving abstinence from food and wine, a sacrifice or gift to the god, and a

nocturnal “incubational” period.1

Aristotle stood at the portal between mythical and modern horizons of thought, and was a

prime motivating agent in propelling medicine, not just philosophy, through that portal.

As a natural philosopher, Aristotle’s influence on medicine is two-pronged – first in

terms of immediate causation – his influence on his own students and their intellectual

descendents – and secondly in terms of indirect causation – his influence on medical

debates raging today.

The shift

The Sicilian philosopher (and some speculate physician) Empedocles, whose life

straddled the sixth and fifth centuries B.C., is credited with the notion that everything

existing is composed of four elements – earth, air, fire, and water.2 Alcmaeon of Croton

(~470 B.C.) held to a similar natural scheme, claiming an equality of powers is

responsible for health – moist and dry; cold and hot; bitter and sweet.

An interesting schism over this model developed with which Aristotle was to contend.

Following Empedocles’ lead, Plato ascribed to a four-element theory, having placed

emphasis on universal principles, including the Forms. Alcmaeon, however, believed that

investigation and even dissection, not just philosophy, was necessary to understand the

body (MI, 192).3 Aristotle was to wed Plato’s and Alcmaeon’s two strains of thought.

Aristotle’s influence on Greek medical practice and thought

Aristotle was born 384 B.C. in Stagira, Thrace. His father Nicomachus was a member of

the guild of the Asclepiadae, and his mother Phaestis was a member of the Asclepiad

family. His father was court physician to the King of Macedon, the grandfather of

Alexander the Great. Indeed, it is recorded that Aristotle served for three years as tutor to

Alexander.4 According to Claudius Galen, the Asclepiad families trained their sons from

childhood in anatomy on top of the basic foundation of reading and writing, a course of

study that Aristotle may himself have experienced.5

Nonetheless, Aristotle broke away from his father’s profession, and entered Plato’s

Academy at age eighteen. Like Plato, Aristotle was firmly committed to the belief that

the first principles of medicine should derive from general philosophical principles. The

principles Aristotle adopted included the four-element theory of earth, air, fire, and water.

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(He also subscribed to a fifth, non-terrestrial element, the “quintessence” or “ether,”

which he believed existed in the heavens.) However, Aristotle’s beliefs additionally

incorporated the criterion of “sensibility” – to him the four-element theory had to meet

standards of theory and observation.

Plato contended that regularities in the patterns of nature are explainable by geometrical

relations between the surfaces of bodies that symbolically represent the four elements.

Aristotle felt that it is impossible for corporeal bodies to be made out of planes. An axiom

of scientific explanation had been violated, he contended: “Perceptible things require

perceptible principles, eternal things eternal principles, corruptible things corruptible

principles” (De Caelo (“On The Heavens”) 306a9-12).6 For Aristotle, the properties of

matter that counted were hot and cold, dry and moist, heavy and light, hard and soft,

viscous and brittle, rough and smooth, coarse and fine (GR, 155). While Aristotle

subscribed to a principled reality, these principles allegedly derived more from the

perception of the world than from the mind. In that sense, his thought was in harmony

with Alcmaeon’s.

Aristotle moved these ideas in two scientific directions. First, he tried to account for

change in the elements. Aristotle realized that matter’s ability to go “crunch” was in need

of explanation. According to him, change between the elements comes about by

transformation of a contrary into its opposite – water turns into air when heat overcomes

cold; air turns into fire when the moist is overpowered by the dry. These simple ideas

bear an uncanny resemblance to modern thermodynamic and convection principles. They

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may also have had an influence on Western contemporary philosophy. Martin Heidegger,

citing Henri Bergson’s thesis “Quid Aristoteles de loco senserit” (Aristotle’s conception

of place), claimed that Bergson’s view of time was in essence determined by Greek

thought.

The second scientific direction was a deepening of the fourfold theory of the elements

with physiologic observation. The body fluids or humours were composed of varying

proportions of blood (warm and moist); phlegm (cold and moist); yellow bile (warm and

dry); and black bile (cold and dry) (MI, 195).2 Disequilibrium in their balance caused

disease, described in three major phases of progression by Hippocrates (MI, 210).

Aristotle elaborated on the function of the elements with respect to the body. Air is taken

into the body to cool the “innate heat” or pneuma within. Moistness is associated with the

watery composition of the tissues. He describes the semen as “wet and waterlike” (GR,

159). Beyond the substance of the body, the form has “homogeneous parts” (flesh, bone,

and blood) and “heterogeneous parts” (e.g., the face, hand, and foot) (CW, 996-7).

Together, the material and formal levels represented the “three degrees of composition”

of the human body (CW, 1005). This nuanced system carried Aristotle beyond the purely

philosophical domain and into the realm of medical science.

Aristotle’s empirical side

It is little surprise that Aristotle’s approach towards the elemental principles would learn

towards the natural. Diogenes Laërtius cites two separate works by Aristotle on anatomy,

and two treatises by him on medicine. Aristotle in some twenty instances

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straightforwardly refers to his Anatomai or “Dissections.” This lost work, variously

described by authors as existing in seven to eight volumes, was apparently an illustrated

handbook with zoological commentary (GR, 149).7 Aristotle’s writings indicate that he

dissected many animals (a practice he may have inherited from Alcmaeon) and achieved

considerable skill as a comparative anatomist. He is considered by some to have been the

first individual to have used dissection extensively; by others, to be the first natural

historian.

Aristotle’s empirical investigations moved in the direction of both the human and natural

worlds. Exploration of natural history was done on the isle of Lesbos, where Aristotle

wrote three volumes: History of Animals, Generation of Animals, and Parts of Animals.

In these works he described embryological development in fish and sharks, ruminants’

four-chambered fore-stomachs, and the distinctive sutures of the human skull. Aristotle’s

progressive descriptions of the heart went considerably beyond the Hippocratic writings

(Hippocratic physicians did not dissect human beings), and later provoked a response

from Galen about Aristotle’s method of dissecting as he went about testing the

philosopher’s ideas.

In a very unique way, Aristotle was able to respect both principled philosophy and

observational natural philosophy. Both perspectives on nature led to a personal

exploration of the causes of things, and his classic description in Physics, Book II of the

various causes: material (natural “substance” and “substrata”); formal (the “shape and

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form of things”); efficient (the “proximate source of change or rest”); and final (the “end

or purpose of a thing”).8

Direct influence on medicine and biology

Aristotle’s tenets were transmitted by way of training students in the Lyceum and his

significant body of writings. Chief among the medical advocates within the Lyceum was

Diocles. Like Aristotle, he ascribed to the four-element theory and believed that the

purpose of respiration was to cool the innate heat (which he contended took place through

the pores of the skin as well as the nose and mouth). He is likely to have played an

influential role in the development of anatomy and physiology within the school.

Aristotle’s successor at the Lyceum, Theophrastus, maintained the biologic tradition by

writing a series of books on botany, the History of Plants and Causes of Plants, which

continued as the most significant contributions to the field even in the Middle Ages (GS,

51-2). Terms coined by Theophrastus, such as carpos (fruit) and pericarpion (seed

vessel), are still being used today.

Claudius Galen, considered to be the most important contributor to medicine in the

several centuries occupying and following the Roman period, was measurably influenced

by Aristotle’s work. While Galen produced many commentaries on the Hippocratic

treatises, his philosophical ideas originate mainly from Aristotle, with some input from

Plato and the Stoics.2 Aristotle’s principle of efficient causes is well exemplified in

Galen’s system of thought. Galen was especially interested in the causation of diseases

and the influence of the environment on people’s health. Like Aristotle, Galen depended

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on dissection for his discoveries. He agreed with Aristotle’s idea of a functional form

behind natural bodies such as organs, as well as his views of the four humours, having

extended them into psychological types – the phlegmatic, sanguine, choleric, and

melancholic. He valued both reason and observation, but felt logic should be carefully

used to confirm hypotheses.

Aristotle and Galen greatly influenced the orbit of philosopher-physicians during the 10th

and 11th centuries (MI, 313). Persian born physician Avicenna (Arabic: Ibn Sina, 980 –

1037 AD) incorporated Aristotelian logic and Galen’s teachings into medical diagnosis

and treatment. It is said that as a teenager, he read Aristotle’s Metaphysics forty times

before comprehending it through an illuminating commentary by al-Farabi. Like Galen,

Avicenna held to Aristotle’s four humour types, which he associated with signs,

symptoms, and treatments. Avicenna’s The Canon of Medicine began to move humour

theory closer to modern medicine, and served as the standard medical text in Europe

through the 17th century (MI, 310). In The Book of Healing Avicenna recommended two

epistemologic methods: Aristotle’s method of induction, and the method of

experimentation.

Lying at the crossroads between classic and Medieval medical thought and the modern

outlook was a pupil of Avicenna’s, Averroes (Arabic: Ibn Rushd, 1126 – 1198 AD), also

known as “The Commentator” (MI, 313). Living in Cordoba, Spain (then Al-Andalus),

Averroes was commissioned by the Sultan to broadly examine Aristotle’s writings, which

he compiled into three diverse commentaries. Like Aristotle, Averroes believed in and

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wrote about the importance of dissection, though for him it was a means to strengthen

faith.

Aristotle’s influence on medicine during the Scientific Revolution permeated the work of

English physician William Harvey (1578 – 1657), a self-avowed devotee of Aristotle

since his medical training in Padua.9 It is thought that his hunch or hypothesis on the

circularity of the bloodstream was based on the Aristotelian principle of circular motion

(NL, 4, 15). Harvey in his De Motu Cordis even quotes Aristotle’s depiction of the water

cycle. Despite the use of prior principles concerning circularity and purity of blood (NL,

14, 17; AP, 270), Harvey admonished his readers to weigh all that he was saying in the

light of experience, a conviction grounded in Aristotle.

Aristotle’s active observational approach clearly passed to his followers and their

intellectual progeny. To this day the elucidation of causal mechanisms is of utmost

importance in medical practice and health research.

Indirect influence on medicine and biology

A more indirect influence on medical theory and practice might be traced to Aristotle’s

notion of a final cause. Aristotle explains, “Then there is what is a cause insofar as it is an

end; this is the purpose of a thing; in this sense health, for instance, is the cause of a

man’s going for a walk” (Physica II 194b33-35).8 Closely associated with the notion of

purpose is that of chance, for random chance would seem to indicate that the behavior of

a body or bodies are not governed by some purpose. Aristotle questions the role of

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