-The aim of this article is to critically discuss the role played by discourses and practices of language diversity in the framework of the 'reason of the state'. This article investigates the way the 'will to know' about language diversity has worked in Brazil, from its colonial period until nowadays, related to the colonial device and the state government. In order to do so, we fi rst present Michel Foucault's conceptions of reason of state and of the birth of the modern states in Europe in relation to the religious and scientifi c domains. Then, a panoramic analysis of the discourses and practices of language diversity in the Brazilian context since the 16 th century is offered. We argue that that the interest in linguistic diversity and its promotion does not mean that discursive diversity is also being promoted, since the existence of language diversity does not imply, necessarily, the existence and protection of a variety of cultures, ways of being, thinking and acting in the world.