Cratylus (ˈkrætɪləs ; Κρατύλος, Kratylos) is the name of a dialogue by Plato. Most modern scholars agree that it was written mostly during Plato's so-called middle period. In the dialogue, Socrates is asked by two men, Cratylus and Hermogenes, to tell them whether names are "conventional" or "natural", that is, whether language is a system of arbitrary signs or whether words have an intrinsic relation to the things they signify.
The individual Cratylus was the first intellectual influence on Plato (Sedley). Aristotle states that Cratylus influenced Plato by introducing to him the teachings of Heraclitus, according to MW. Riley.
The subject of Cratylus is on the correctness of names (περὶ ὀνομάτων ὀρθότητος), in other words, it is a critique on the subject of naming (Baxter).
When discussing an ὄνομα (onoma ) and how it would relate to its subject, Socrates compares the original creation of a word to the work of an artist. An artist uses color to express the essence of his subject in a painting. In much the same way, the creator of words uses letters containing certain sounds to express the essence of a word's subject. There is a letter that is best for soft things, one for liquid things, and so on. He comments:
the best possible way to speak consists in using names all (or most) of which are like the things they name (that is, are appropriate to them), while the worst is to use the opposite kind of names.
One countering position, held by Hermogenes, is that names have come about due to custom and convention. They do not express the essence of their subject, so they can be swapped with something unrelated by the individuals or communities who use them.
The line between the two perspectives is often blurred. During more than half of the dialogue, Socrates makes guesses at Hermogenes' request as to where names and words have come from. These include the names of the Olympian gods, personified deities, and many words that describe abstract concepts. He examines whether, for example, giving names of "streams" to Cronus and Rhea (Ροή – flow or space) are purely accidental.