c. 450 BCE

The Four Elements

Empedocles (c. 490–430 BCE), Plato (c. 428–c. 347 BCE), Aristotle (384–322 BCE), Abū Mūsā Jābir ibn ayyān (c. 721–c. 815)

Thanks to the Greek philosopher Empedocles and his mid-fifth-century BCE poem On Nature, for almost two thousand years people thought that there were only four fundamental elements—earth, air, fire, and water—and that the composition of everything in the world depended on the varying proportions of them. So, why is this a milestone in chemistry? In fact, Empedocles was quite correct in the idea that there are such fundamental substances (which he called roots), and compared to some other philosophical systems, his conclusions were quite a leap forward. The world wasn’t made up of just one substance that somehow manifested itself to us in different ways, and it wasn’t made up of uncountable different substances, either. Rather, the world contained a countable number of basic building blocks from which everything else was assembled. From that standpoint, the difference between the four classical elements and the modern periodic table is merely a matter of degrees.

It was Plato who introduced the term element, and his famous student Aristotle worked out a scheme by which the characteristics of everything else could be understood as mixtures of them, giving each element two of four sensible qualities (e.g., air: wet-hot, earth: dry-cold) and adding a superior fifth element he called aether. Later philosophers introduced more elements and complexities to try to explain more phenomena, and the entire scheme of thought led eventually into alchemy via the writings of the Persian polymath Abū Mūsā Jābir ibn ayyān (a.k.a. “Geber”) more than a thousand years later.

This is an early example of reductionism: the search for knowledge by breaking things down into smaller and smaller units in the hope that fundamental truths will eventually be revealed. (In effect, the scientist asks, “OK then, what’s that made of?” over and over.) Reductionism doesn’t always work—some very important effects only show up when you start going back up the scale. (A living cell is far more than the sum of the chemical elements inside it, for example.) But reductionism is still a powerful technique that has long helped to advance chemistry and the other sciences.

Earth, air, fire, and water: the building blocks of the world for two thousand years.