If men needed speech in order to learn to think, they had a still greater need for knowing how to think in order to discover the art of speaking.
Gist of Idea
Language may aid thinking, but powerful thought was needed to produce language
Jean-Jacques Rousseau (Discourse on the Origin of Inequality , Part I)
I take language to be a consequence of the emergence of meta-thought in humanity, so I thoroughly endorse Rousseau's view. The idea that rationality, and even consciousness, are mainly facilitated by language strikes me as quite wrong.
Rousseau,Jean-Jacques: 'The Basic Political Writings', ed/tr. Cress,Donald A. [Hackett 1987], p.49