Every word gains meaning only as we say other words, in this case, the words surrounding it in its sentence. Erasure is the idea that words are inadequate because they have no necessary relationship to the things they signify, yet they are all that we have, so they are necessary for communication. Yet, it is at their disappearance, when we have moved to other words, that the words gain their meaning. While Derrida's criticism reaches to the fundamentals of language itself, much postmodern thought is more concerned with social criticism. Since postmodern thinkers are critical of western thought, it is natural that they would be critical of the social systems western thought has engendered.
Critical theory attempts to develop thoroughgoing criticisms of western society and ideology.
Though often unacknowledged, critical theory continues to owe a tremendous debt to Marxist thought. Critical theory presupposes many Marxist notions, including assumptions that a dominating class exists by oppressing other classes in society. Michel Foucault was one of the most recognized late twentieth century social critics. Foucault was a homosexual who saw western society as dominated by a power struggle between central epistemes and those who society marginalized. To enforce its control over society, the central episteme used all available communication channels to define and create truth for society.