The history of the concept of ideology has often been analysed.¹ None the less, there is some point in commenting upon this history here, since I shall argue that it is indispensable to an evaluation of how "ideology" should be understood in the social sciences. I shall concentrate only upon certain phases in the evolution of the notion: its usage by Marx, still the inevitable point of departure for any contemporary discussion of ideology; Mannheim's version of the 'sociology of knowledge"; and the more recent accounts of ideology suggested by Habermas and Althusser.