Cratylus

A dialogue about whether names are correct by nature or by convention, often called the first work of Western philosophy of language. Hermogenes holds that a name is simply whatever a community agrees to call something; Cratylus holds that every name has a natural correctness. Socrates first gets Hermogenes to reject Protagoras' relativism, then argues that a name is a tool for teaching and separating things, made by a skilled name-giver. There follows the longest section, a long run of playful and often fanciful etymologies of the names of gods, heavenly bodies and virtues, ending with the claim that single letters imitate qualities. Socrates then turns on Cratylus: names can be good or bad likenesses, convention must play some part, and we cannot learn about things by studying their names. The dialogue closes by setting the stable objects of knowledge against Heraclitean flux, without settling the matter.

It asks questions about words and meaning that still drive philosophy of language, and its mock etymologies are a warning against arguing from the history of a word to the nature of a thing.