Parmenides is one of the most significant of the pre-Socratic philosophers. His only known work, conventionally titled On Nature, is a poem, which has only survived in fragmentary form. Approximately 160 lines of the poem remain today; reportedly the original text had 3,000 lines. It is known, however, that the work originally divided into three parts:
- A proem (Greek: προοίμιον), which introduced the entire work,
- A section known as "The Way of Truth" (aletheia - ἀλήθεια), and
- A section known as "The Way of Appearance/Opinion" (doxa - δόξα).
The proem is a narrative sequence in which the narrator travels "beyond the beaten paths of mortal men" to receive a revelation from an unnamed goddess (generally thought to be Persephone or Dike) on the nature of reality. Aletheia, an estimated 90% of which has survived, and doxa, most of which no longer exists, are then presented as the spoken revelation of the goddess without any accompanying narrative.
Parmenides attempted to distinguish between the unity of nature and its variety, insisting in the Way of Truth upon the reality of its unity, which is therefore the object of knowledge, and upon the unreality of its variety, which is therefore the object, not of knowledge, but of opinion. In the Way of Opinion he propounded a theory of the world of seeming and its development, pointing out however that, in accordance with the principles already laid down, these cosmological speculations do not pretend to anything more than mere appearance.
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