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.

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.

Although he denounces a wide range of contemporary philosophical schools of thought, Horkheimer asserts that these trends are epitomized in positivism, a term he defines broadly.

He concludes, If by enlightenment and intellectual progress we mean the freeing of man from superstitious belief in evil forces, in demons and fairies, in blind fate – in short, the emancipation from fear – then denunciation of what is currently called reason is the greatest service we can render.