First published in 1947 under the title "Eclipse of Reason," this book is a key text of Critical Theory. It unfolds a historical process that has already been reconstructed in the thematically closely related Dialectic of Enlightenment: the decline of a human reason understood as "objective," which sets values and goals. In its place arises a purely formal reason focused solely on mere effectiveness, which renders any comprehensive notion of happiness for society as meaningless.