Literature on the education of the deaf people in France usually identifies the Rousseauist notion of perfectibility as significant to understand the attempts of the nineteenth-century oralists to suppress signed language in favor of speech. However, the notion of perfectibility has often been mistaken as a synonym for « ideology of progress », as scholars have focussed on the reinterpretations of Rousseau’s thought rather than on his texts, ignoring the references to deafness in his works. The purpose of this article is to show that Rousseau uses the case of deafness as a linguistic proof of man’s unique capacity for getting either better or worse.