The dissertation The language in Plato’s Cratylus intends, through the analysis of the theses presented by Plato in the Cratylus about the correctness of names and their refutations, make a reflection on how Plato will direct the philosophical investigations in relation to language; and also highlight the importance of such dialogue not only to Platonic thought, but also for the preservation of some of the first discussions about the language in the history of human thought. This dissertation is the result of a more general research that seeks to analyze the relationship in the context of Greek philosophy, between philosophy and sophistry (rhetoric). Among the commentators is common to find the idea that in the fifth century BC and early, there was, so to speak, a battle, begun by Plato, between philosophy and sophistry, seeking the intellectual monopoly of Greek society. And a discussion on this capital clash between philosophy and sophistry with regard to the functions, powers and limits of the logos. So, in analyzing the Cratylus is possible to identify particular with respect to such Platonic discussion of the language.