Eclipse of Reason is a 1947 book by Max Horkheimer, a German philosopher and sociologist who was a key figure in the Frankfurt School of critical theory. In the book, Horkheimer argues that in modernity the concept of reason has been reduced to a mere instrument for achieving practical goals, rather than a means of understanding objective truth. He contends that this "eclipse of reason" has led to the rise of authoritarianism, as well as the dominance of a manipulative "culture industry" that serves the interests of those in power. Horkheimer asserts that to counter these trends, it is necessary to develop a more substantive and critical form of reason that is grounded in a commitment to human emancipation and the pursuit of a more just society.