Democritus

hat Leucippus thought about cosmology and its atomic structure, is generally assumed to be identical with the views of his student Democritus (c. 460-357 BC), who elaborated further on the subject, being the one mostly quoted on it. Diogenes Laertius gives a long list of books written by Democritus, dividing them into the groups ethics, virtue, physics, "no head", mathematics, literature and music, and the arts. Most famous were The Great Diacosmos (world order) and The Lesser Diacosmos, though Diogenes says the former is by some attributed to Leucippus.

     Although Democritus made the theory of atoms a basis for all things in the world, including for example color as a difference in surface of the atoms and taste a difference in shape, he held, according to Aristotle, a modest view toward learning: "Either there is no truth or it is concealed from us." This may be a slight misinterpretation of his thoughts on perception:

     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.

     Since all the senses work on inflow of atoms carrying their respective characteristics, to Democritus it was obvious that one could not say to know reality as it was, but only as its fragments reached its observers. Regarding knowledge itself, he seems not to have been as modest as Aristotle has it.

     No more than his teacher did Democritus involve the gods in his cosmos, and so also with him it can be said that we have no statement of his swearing to it, but at least in all cosmological matters he should be regarded as an atheist.

Literature
Aristotle, Metaphysics, 1009b, translated by Hugh Lawson-Tancred, London 1998.
Freeman, Kathleen, Ancilla to The Pre-Socratic Philosophers, Oxford 1952.