Democritus (ca.
Circa , usually abbreviated c. or ca. , means "approximately" in the English language, usually referring to a date...

 460 BC – ca. 370 BC) was an Ancient Greek philosopher born in Abdera, Thrace
Abdera, Thrace
Abdera was a city-state on the coast of Thrace 17 km east-northeast of the mouth of the Nestos, and almost opposite Thasos. The site now lies in the Xanthi peripheral unit of modern Greece. The municipality of Abdera, or Ávdira , has 18,573 inhabitants...

, Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

. He was an influential pre-Socratic philosopher
Pre-Socratic philosophy
Pre-Socratic philosophy is Greek philosophy before Socrates . In Classical antiquity, the Presocratic philosophers were called physiologoi...

 and pupil of Leucippus
Leucippus or Leukippos was one of the earliest Greeks to develop the theory of atomism — the idea that everything is composed entirely of various imperishable, indivisible elements called atoms — which was elaborated in greater detail by his pupil and successor, Democritus...

, who formulated an atomic theory
Atomic theory
In chemistry and physics, atomic theory is a theory of the nature of matter, which states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity...

 for the cosmos.

His exact contributions are difficult to disentangle from his mentor Leucippus, as they are often mentioned together in texts. Their speculation on atoms, taken from Leucippus, bears a passing and partial resemblance to the nineteenth-century understanding of atomic structure that has led some to regard Democritus as more of a scientist than other Greek philosophers; however their ideas rested on very different bases.

We know nothing accurately in reality, but [only] as it changes according to the bodily condition, and the constitution of those things that flow upon [the body] and impinge upon it.

Freeman (1948), p. 142

Medicine heals diseases of the body, wisdom frees the soul from passions.

Freeman (1948), p. 149

Coition is a slight attack of apoplexy. For man gushes forth from man, and is separated by being torn apart with a kind of blow.

Freeman (1948), p. 150

Man is a universe in little [Microcosm].

Freeman (1948), p. 150

Good breeding in cattle depends on physical health, but in men on a well-formed character.

Freeman (1948), p. 151

Many much-learned men have no intelligence.

Freeman (1948), p. 152

Immoderate desire is the mark of a child, not a man.

Freeman (1948), p. 152

[I would] rather discover one cause than gain the kingdom of Persia.

Freeman (1948), p. 155

Men have fashioned an image of Chance as an excuse for their own stupidity. For Chance rarely conflicts with intelligence, and most things in life can be set in order by an intelligent sharpsightedness.

Freeman (1948), p. 155