Parmenides of Elea, Presocratic philosopher, c . 515–post-450 BCE

Parmenides of Elea is one of the most profound and challenging of the early Greek philosophers. He wrote a didactic poem treating metaphysical and cosmological themes presented in the form of a mystical revelation. It comprised a proem describing his journey to the Halls of Night, where a goddess greets him and presents this revelation in two main parts, which have come to be known as the Way of Truth and the Way of Opinion. The Way of Truth presents a tightly structured sequence of arguments that What Is must be “ungenerated and deathless, | whole and uniform, and still and perfect” (28B8.3–4 DK). The Way of Opinion comprised a cosmology based on the elemental principles Light and Night that contained numerous innovations, including identification of the sun as the source of the moon’s light. Parmenides’ thought inspired diverse reactions and appropriations in antiquity, and both its details and ultimate significance have continued to be intensely controversial. Modern interpretations divide into three main types: those that view Parmenides as a strict monist who denied the existence of the sensible world, those that view him as providing a higher-order characterization of the principles of any acceptable cosmology, and those that understand him as pursuing the distinctions between necessary being, necessary non-being or impossibility, and mutable or contingent being.