In this article we will examine some connections between criticism of Adorno and Horkheimer to instrumental reason limited to the book Dialectic of Enlightenment and the genealogical critique of Nietzsche to the "will to truth ", a theme explored in several books. Then resume the reading of Habermas in The Philosophical Discourse of Modernity on a Nietzsche’s radical critique to modern rationality, in order to examine two points: 1) What arguments support the thesis of inconsistency and lack of foundation of Nietzsche's genealogical critique? 2) why Habermas claims that the heirs of Nietzschean critique repeat this inconsistency, including the very critical of Adorno and Horkheimer? We intend to demonstrate, unlike Habermas, Adorno and Horkheimer in demythologization program of instrumental reason resume Nietzschean critical project aiming to build a new positive and demythologized meaning for enlightenment.