A historical doctrine, not a description of nature
For many centuries, educated people in the Greek, Roman, Islamic and Latin Christian worlds explained nature with a fourfold scheme: four elements, four basic qualities, four bodily humours and, in many versions, four seasons and four directions. This article traces how those schemes developed and how thinkers tried to give them a geometrical shape. They are presented here as historical doctrine. Modern chemistry and medicine do not use them, and nothing in this article should be read as describing how the world or the body actually works.
From Empedocles to Aristotle
The earliest clear statement of four basic substances is attributed to Empedocles, a Greek thinker of the fifth century BCE. He spoke of four “roots” of things, fire, air, water and earth, which were mixed and separated by two forces he called Love and Strife. Earlier thinkers had favoured a single underlying substance, such as water or air, so a plurality of four was a compromise that explained change as mixture.
Aristotle in the fourth century BCE gave the scheme a more systematic shape. He paired two opposite qualities in four combinations:
| Element | Qualities |
|---|---|
| Fire | hot and dry |
| Air | hot and wet |
| Water | cold and wet |
| Earth | cold and dry |
Because elements share one quality with each neighbour, Aristotle argued that they could change into one another: water heated becomes air, for example. He also placed the elements in natural places, with earth at the centre and fire at the outer edge, and added a fifth substance, often called aether, for the heavens. The fifth element is the reason later writers spoke of a “quintessence”.
The idea of tying this scheme to number had precedent. Pythagorean tradition valued the number four as the base of the tetractys, and some later writers associated the four with the first four numbers of that figure. Which of these links were made by early thinkers, and which by later commentators, is difficult to say.
Humours, seasons and directions
Medicine added another set of fours. The Hippocratic collection includes a treatise, On the Nature of Man, which describes the body as containing blood, phlegm, yellow bile and black bile, and links health with their balance. The physician Galen in the second century CE developed this into a detailed system that dominated medicine for well over a thousand years.
Later writers gradually lined up the sets of four so that they matched, and the result was a grid that was easy to memorise:
- blood: air, hot and wet, spring
- yellow bile: fire, hot and dry, summer
- black bile: earth, cold and dry, autumn
- phlegm: water, cold and wet, winter
Details varied between authors. Some assigned the seasons differently, and the pairing with life stages and temperaments was added at different times. Four directions and four winds were also folded into the scheme in many medieval diagrams, which is why a circular layout with the elements at the cardinal points became a standard picture. This habit of making each system match the others reflects a belief in correspondence between the large world and the small, the macrocosm and the microcosm, which was more a way of thinking than an experimental result.
Astrology used a related device. The signs of the zodiac were divided into four groups of three, each assigned an element, and this is why the idea of twelve in astrology so often appears with fire, earth, air and water labels. As with the rest, it is a convention of that tradition.
The geometrical connection
Geometry entered in two main ways.
Shapes for the elements. In the Timaeus, Plato assigned a regular solid to each element, an idea about which a separate article on the Platonic solids gives the details. The point to note here is that it was an attempt to reduce the four elements to geometry, so that their behaviour followed from the shapes of their smallest parts.
Diagrams. Medieval scholars drew the elements, qualities and humours as squares or circles divided in four, with lines crossing to show the oppositions. A common arrangement placed hot against cold and wet against dry along the crossing axes, so that the four elements sat at the corners of a square. Diagrams of this kind appear in manuscripts that explain the order of nature and the medieval calendar systems, and they show how neat the scheme seemed when drawn. A reader looking at such a figure sees why people found it persuasive: it pulled together physics, medicine, seasons and sky in one image.
The cross shape that these diagrams make is related to, but separate from, the ritual uses of the square and cross in building, which are treated elsewhere.
Other traditions of elements
Fourfold schemes were not the only ones. Buddhist texts often speak of four great elements, earth, water, fire and wind, as the constituents of material things, and other Indian systems add space to make five. Chinese thought developed a scheme of five phases, wood, fire, earth, metal and water, which sits alongside yin and yang, is not the same kind of thing as the Greek elements, and operates through cycles of generation and overcoming rather than through simple pairs. The existence of these different counts is a useful reminder that four was a choice made within particular traditions, not a number nature imposed on all of them.
How the doctrine faded
The fourfold system lasted because it fit so many observations loosely. It began to give way between the seventeenth and nineteenth centuries, as experiments showed that air and water are not simple elements and that diseases have specific causes. The word “humour” survives in everyday speech, as does the idea of a “sanguine” or “melancholic” temperament, but only as a trace of the old vocabulary. Seen historically, the doctrine is a serious attempt, using the knowledge available, to find order in the world, and its habit of reaching for the number four tells us more about its builders than about nature.