His contemporaries—he was born about 460 BC in Abdera, Thrace—called him the “laughing philosopher” because, in ethics and politics, he placed great value on optimism and cheerfulness. Modern historians of philosophy and science remember him as the first to establish the atomic—or atomist—theory, which he built upon the foundation of his teacher Leucippus. Going hand in hand with this materialist view of the world was Democritus’ empiricism, which has led many to dub him the “father of modern science.”
Democritus theorized that atoms are the smallest bodies from which everything in the world is composed. While physically indivisible and indestructible, atoms, he believed, were nevertheless divisible geometrically. Between the individual atoms that form everything, Democritus envisioned the empty space of the infinite void through which the atoms continuously move. He attributed the characteristics of differing forms of matter—iron, water, air, and so on—to differing characteristics of the atoms that make them up. Iron atoms were strong and solid, their surface equipped with hooks that create strong bonds. Water atoms were slippery in nature, and the atoms of air were light and whirling. Democritus’ universe of atoms and voids was not teleological. That is, its regularity and patterns were the structural result of the underlying atoms themselves and not the product of a transcendent divine plan.
Little is known of the life of Democritus, but it is generally accepted that he was a citize of the Thracian city of Abdera, although a dissenting minority suggests he was from Miletus. It is known that his teacher (or, perhaps, colleague) was Leucippus, and some speculate that he was also associated with Anaxagoras. None of Democritus’ writings survive.
Diogenes Laertius, the third century AD biographer of the ancient philosophers, compiled an extensive list of works by Democritus in fields ranging from ethics to physics, mathematics, music, and cosmology. Modern scholars have doubts about the authenticity of his ethical works, and all that is known of his writing comes from the reports of others, including Aristotle, a critic of his views, but one who devoted a monograph to him, of which only quotations by third parties survive.
Related to Democritus’ theory of atomism is his theory of perception, which holds that eidôla (images) are exquisitely thin layers of atoms, which continually slough off from the surfaces of things, are carried through the air, and enter the eye, where their impact causes the sensation of sight. Atomists following Democritus theorized that these atomic films contract and expand. The expanded films are too large to enter the eyes, so that only the contracted films can be visually perceived.
Aristotle reports that Democritus envisioned the soul (psyche) as composed of fire atoms. This is consistent with the ancient equation of life with heat and with the notion, also popular in antiquity, that the soul was responsible for motion in living beings. No atoms, they argued, are more mobile than those of fire. Apparently, Democritus believed that the movement of the fire atoms of the psyche was also responsible for thought, so that his theory of knowledge holds that the phenomena of thought are caused by images that impinge from the outside. He further held that perception is due, essentially, to bodily changes caused by external influences.
Ancient authorities ascribe various works of mathematics to Democritus, along with treatises on biology and cosmology. None of these survive, except for the geometric principle that cones whose base and height are the same have one-third the volume of a cylinder of the same base and height. Similarly, a pyramid whose base and height are the same have onethird the volume of a prism with the same base and height.
As for the philosopher’s ethics and politics, all that survives are individual maxims, whose authorship is disputed and whose intellectual relation to one another is doubtful. In short, Democritus left no systematic philosophy of ethics or politics. He is believed to have died at about ninety, which would have been approximately in the year 370 BC.
