(Student Guide to World Philosophy)

Although there are no extant fragments of the writings of Pythagoras, his views were influential in the ancient world and have been referred to by a number of philosophical writers, among them Plato, Aristotle, Porphyry, and Diogenes Laërtius. As one might expect, the accounts are not entirely consistent, and it is often difficult to determine precisely or even approximately what view Pythagoras held on a question under discussion, but there is a body of beliefs that critics generally attribute to Pythagoras or to his followers. The followers are generally assumed either to have inherited the master’s views or to have been inspired by his philosophy and practice to develop their ideas along lines that have a distinctive inherited character.

Pythagoras (like many ancient Greek philosophers) did not distinguish his metaphysical convictions from his beliefs about the physical world: His ontology (theory of being), cosmology (theory of cosmic origin and development), epistemology (theory of knowledge), theology, and ethics appear to be grounded in certain abstract mathematical ideas and beliefs and to be interrelated.