The Greek philosopher Parmenides (active 475 BC) asserted that true being and knowledge, discovered by the intellect, must be distinguished from appearance and opinion, based on the senses. He held that there is an eternal One, which is timeless, motionless, and changeless.

Parmenides was born in Elea in southern Italy in the late 6th century B.C. Socrates, in Plato's Thaetetus, tells how as a young man he met Parmenides and Zeno on their visit to Athens about 450. Little else is recorded about the details of Parmenides's life. He wrote a didactic poem in hexameters, the meter of the Homeric epics and of the oracular responses at Delphi, in which he described a divine revelation. Fragments of the poem remain and provide a fair idea of what he attempted to prove, although even when the entire poem was extant there were problems of interpretation.

The poem consists of a...