Democritus was a Greek philosopher born around 460 BC. Though most of his texts were lost, we are able to learn about his ideas through the works of Aristotle. There ideas rivaled one another. Leucippus mentored Democritus during his travels in Greece. Most people refer to Leucippus as one of the first atomists, the idea that the universe is composed of atoms.

Democritus was a prominent figure in atomic theory. He theorized that all material is made up of atoms. He said that atoms were so small that they could not be reduced to anything else. He theorized that the universe is made up of the space with atoms, or the Being, and the vacuum that is absent of atoms. He called this empty space the void. He pictured atoms as mostly homogeneous. He thought the reason things look different and feel different to us is because they are made up of different configurations and combinations of atoms. He theorized that because everything is made of these infinite atoms nothing really dies. Everything just changes form. This idea is very similar to the popular concept of today that matter cannot be created or destroyed.

Democritus said theorized that motion has always existed. He said that the universe began with atoms moving in all directions. Then, the atoms began to collide with similar atoms to form larger entities. Democritus did not believe the universe formed because of a purpose. He only believed it happened because of necessity. He theorized that the Void and the Being were infinite and expanded in all directions. He also believed that there had to be infinite other worlds that consisted of atoms.

Democritus thought that his theory of atoms applied to emotions as well. He thought that sensations came from when atoms outside of oneself came in contact with the soul. Democritus thought that atoms of the soul can only be affected by other atoms. He was also the first who attempted to explain color. He thought that changes in color were due to different positions, different than shape, of atoms. Democritus thought that the color white came from flat atoms that caused no shadow, while black came from rough atoms.

Democritus came from a wealthy family. He spent all his inheritance on traveling to the east in search for knowledge. This access to resources allowed him to gain knowledge and meet other philosophers of the time. From his accounts, it is possible that he met Hippocrates when he travelled through Greece. The gods were very popular, but Democrites did not believe in them. He believed in his own ethical system which was based on practicality. This is different from a lot of philosophers, because the belief of the gods was so ingrained into the lives of the Greeks. These fundamental differences may be part of the reason why he disagreed with Aristotle.