Democritus

"Nothing exists except atoms and empty space: everything else is opinion."

Time Period: 460-370 BC

Background: Born in Abdera, Thrace, Democritus wrote extensively on the subject of ethics, promoting happiness as the highest good, insisting that it was to be achieved through moderation, tranquility, and freedom from fear. He came to be known as the Laughing Philosopher, for his jovial spirit, in contrast to the pessimistic Heraclitus (the Weeping Philosopher). He based much of his theories from his teacher, Leucippus.

Belief:  Democritus wrote that all things were composed of atoms - small, minute, and indestructible particles of pure matter, with a void between each and every atom. He wrote that atoms were solid, with no internal structure, and that they were different in size, shape, and weight.

Contribution: Although some points of Democritus's beliefs were incorrect (atoms are not completely solid and do not lack an internal structure), he  nevertheless helped us to understand the basic atomic theory of matter. We now know and accept that atoms are indeed the basic building blocks of matter, and that they differ innumerably in shape, size, weight, position, and sequence.