The precursor of the debate about positivism can be traced back to Max Horkheimer's essay ""Der neueste Angriff auf die Metaphysik"" ("The Latest Attack on Metaphysics") published in 1937 that criticizes the logical positivism of the Vienna Circle. The prolonged criticism of positivism led to the formation of two camps: on one side we find critical rationalism advanced by Karl Popper and on the other side there is the critical theory advanced in the Frankfurt School. This view was strengthened by the fact that Popper's main work, "Logic of Scientific Discovery", was published in the main book series of the Vienna Circle. Popper, however, considered himself an opponent of positivism, and his main work was a sharp attack on it.