Critical theory is a school of thought that stresses the reflective assessment and critique of society and culture by applying knowledge from the social sciences and the humanities. As a term, critical theory has two meanings with different origins and histories: the first originated in sociology and the second originated in literary criticism, whereby it is used and applied as an umbrella term that can describe a theory founded upon critique; thus, the theorist Max Horkheimer described a theory as critical insofar as it seeks “to liberate human beings from the circumstances that enslave them.” In philosophy, the term critical theory describes the neo-Marxist philosophy of the Frankfurt School, which was developed in Germany in the 1930s. Frankfurt theorists drew on the critical methods of Karl Marx and Sigmund Freud. Critical theory maintains that ideology is the principal obstacle to human liberation. Critical theory was established as a school of thought primarily by five Frankfurt School theoreticians: Herbert Marcuse, Theodor Adorno, Max Horkheimer, Walter Benjamin, and Erich Fromm. Modern critical theory has additionally been influenced by György Lukács and Antonio Gramsci, as well as the second generation Frankfurt School scholars, notably Jürgen Habermas. In Habermas’s work, critical theory transcended its theoretical roots in German idealism, and progressed closer to American pragmatism. Concern for social “base and superstructure” is one of the remaining Marxist philosophic concepts in much of the contemporary critical theory. While critical theorists have been frequently defined as Marxist intellectuals, their tendency to denounce some Marxist concepts and to combine Marxian analysis with other sociologic and philosophic traditions has resulted in accusations of revisionism by Classical, Orthodox, and Analytical Marxists, and by Marxist-Leninist philosophers. Martin Jay has stated that the first generation of critical theory is best understood as not promoting a specific philosophical agenda or a specific ideology, but as “a gadfly of other systems”.