In the Parmenides, Plato brought his mentor and hero Socrates face to face with Parmenides of Elea, the most imposing and reverend figure of early Greek philosophy. He also introduced Parmenides’ most famous student, Zeno of Elea. Parmenides and his followers were famous for declaring that there is no change: there is only what-is, complete and perfect and unalterable.
In what seems to be the sequel to the Parmenides, the Theaetetus, Plato will confront the other pillar of Presocratic philosophy, Heraclitus of Ephesus. Heraclitus is, moreover, the polar opposite of Parmenides in his philosophical doctrine. According to Plato, he says that everything is changing and nothing remains constant. The world is “everliving fire,” which is kindled and being quenched by turns.[1]
Plato has mentioned his predecessors—to be more precise, Socrates’ predecessors—sporadically in his dialogues. For instance, he engaged with Anaxagoras in the Phaedo, who said that everything in the world is arranged for the best. But in his later works, he occupies whole dialogues explaining and examining, often refuting, the philosophical theories of his predecessors. In the Parmenides and Theaetetus, Plato confronts the two most extreme positions of early Greek philosophy, the view that everything is at rest (Parmenides), and the view that everything is in motion (Heraclitus).
In fact, however, when Plato wrote the Theaetetus, he had already talked about Heraclitus’ theory, tangentially, but at some length. In the Cratylus, a middle dialogue of uncertain date, Plato has Socrates discuss with Cratylus, a well-known Heraclitean of the late fifth and early fourth centuries BCE, and with Hermogenes, a Socratic known to both Plato and Xenophon,[2] Cratylus’ theory of language. Cratylus claims that words have their meaning by nature; Hermogenes argues to the contrary that words have their meaning only by convention, that is, by some sort of social agreement.[3] In the dialogue Socrates explores Cratylus’ claim, offering ingenious though apparently fanciful etymologies for many Greek words, on the assumption that the words have their meanings by nature.
In the process of Socrates’ analyses of words, he uses Heraclitean assumptions. For instance, the etymology of phronēsis ‘wisdom’ is phoras noēsis ‘understanding of motion.’[4] Socrates sees Heraclitus’ theory as having been presented already by Homer and Hesiod, for whom the early generation of gods included Cronus and Rhea, both allegedly named after streams.[5] One of the first deities was Oceanus, the stream that surrounds the disk of Mother Earth and appears as one of the first deities in Hesiod’s theogony.[6]
These associations lead Socrates to say, “Heraclitus, I believe, says that all things pass and nothing stays, and comparing existing things to the flow of a river [potamou rhoēi], he says you could not step twice into the same river.”[7]
After exploring, perhaps playfully, but at great length, the implications of Heraclitean theory and its connections with language and meaning, Socrates suggests the possibility of a Beautiful Itself, a Form of Beauty, that always is what it is, and other similar Forms that might give meaning to phenomena. If such things did not exist, he hints, there could be no knowledge whatsoever of the flux of experience.[8]
[1] Heraclitus fragment 30.
[2] Plato Phaedo 59b; Xenophon Apology 2. Hermogenes was the illegitimate son of Hipponicus, half brother of Callias, host of the congress of sophists portrayed in the Protagoras: Nails 2002: 162-164. On Cratylus, see ibid. 105-106.
[3] Plato Cratylus 383a, c-d.
[4] Plato Cratylus 411d.
[5] Plato Cratylus 402a-c. He presumably connects Cronus to krounos ‘spring’ and Rhea to rheuma ‘stream.’
[6] Hesiod Theogony 126-137.
[7] Plato Cratylus 402a.
[8] Plato Cratylus 439d-440a. The word ‘Form’ idea appears at 439e5.