Is Enlightenment irrational?

Long before "postmodernism" became fashionable, Adorno and Horkheimer wrote one of the most searching critiques of modernity to have emerged among progressive European intellectuals. Dialectic of Enlightenment is a product of their wartime exile. It first appeared as a mimeograph titled Philosophical Fragments in 1944. This title became the subtitle when the book was published in 1947. Their book opens with a grim assessment of the modern West: "Enlightenment, understood in the widest sense as the advance of thought, has always aimed at liberating human beings from fear and installing them as masters. Yet the wholly enlightened earth radiates under the sign of disaster triumphant" (DE 1, translation modified). How can this be, the authors ask. How can the progress of modern science and medicine and industry promise to liberate people from ignorance, disease, and brutal, mind-numbing work, yet help create a world where people willingly swallow fascist ideology, knowingly practice deliberate genocide, and energetically develop lethal weapons of mass destruction? Reason, they answer, has become irrational.