Democritus was born in Abdera, Thrace and lived during the years 460-370 BCE. His biography is related by Diogenes Laertius in his Lives of Eminent Philosophers (as was Epicurus’). He came from a wealthy family and, after the death of his father, he travelled in search of wisdom to Egypt, Ethiopia, India, served Xerxes in Persia, was instructed there by the Magi in astrology, and finally he returned to Abdera where his brother, Damosis, took him in. There, he gave lectures.
He is relevant to us for having been the instructor of Nausiphanes, who later taught atomism to Epicurus. Originally, he was a pupil of Leucippus, of whom little is known and who is credited with being the first atomist.
Democritus contributed so much to the original atomist theory that they’re both considered founders of the atomist school. In fact, he systematized it.
But Democritus’ stream of thought really goes back further than his master Leucippus: he was also reacting against Parmenides’s theory that there is no change or motion, only the all, and that all things are one and the same primal thing. This is obviously false: multiplicity is in evidence everywhere, and so is motion and change.
Parmenides was as much a mystic as he was a philosopher. Philosophy needed to be reconciled with observable facts: this is why the materialist and atomist school emerged. Democritus reasoned that it was obvious that all things were made of some primal thing, and that at some point particles could not be divisible any further (ergo, we would reach an a-tomo, or indivisible particle).
He also reasoned that, for there to be motion, there needed to be a void. If space was filled, nothing would be able to move into it.
By these simple insights, Democritus developed the theory that Epicurus inherited according to which reality is written in the binary language of atoms and the void.
Light-hearted Democritus was also known as the Laughing Philosopher and as the Mocker by his contemporaries because he was always laughing at human nature.
Later, his pupil Nausiphanes argued against the Sceptics, who dismissed the possibility or the need for scientific certainty, and in favor of materialist dogmatism. He reasoned that reality was, in fact, knowable, and that therefore naturalist philosophers needed concise criteria to determine with certainty whether a statement was true or not based on evidence that we can grasp with our natural faculties. For this process, Nausiphanes created the first canon, which Epicurus copied and which later inspired the scientific method.
In celebration of the intellectual grandfather of Epicurus, the 6th Episode of Cosmos includes references to Democritus, who is still today known as the father of modern science.