consider any moving force to be a necessary hypothesis. . . Apparently the early cosmologists did not think of motion as requiring any explanation, and in the Atomist philosophy the eternal movement of the atoms is regarded as self-sufficient (Copleston 74).
Leucippus based his epistemology on sensory observation and the application of logic. He assumed the existence of atoms as a way of explaining the world as seen, and he postulated a void for the atoms to move through as they collided within one another:
These are the only basic realities, atoms and void, and the various universes, of which there may be many, and all individual things in them are simply produced by chance comings-together of atoms in their endless movement in the void (Armstrong 18).
For Leucippus, empty space and the atoms moving through it are the true reality. To arrive at this conclusion, Leucippus built on the ideas and structures created by earlier philosophers who were also attempting to create a comprehensive metaphysics. The approach of Leucippus differs primarily in being mechanistic in nature and in not having an explanation for how this mechanistic universe started.
Protagoras would have an influence on Democritus and Plato. He was part of a group of philosophers known as the Sophists, and they traveled from city to city to offer their services as lecturers for money. Protagoras taught the value of custom and tradition and said there should be a careful and prudent acceptance of such traditions because an understanding of them and the ability to manipulate them are expedient. For Protagoras, all customs were relative rather than absolute, and he saw everything as relative to human subjectivity (Palmer 40). For Protagoras, epistemology involves certain procedural realities that make metaphysics a relative matter and not a matter of absolute truth, which cannot be perceived without recourse to relativism and subjectivity.
Protag...