Louis Althusser's "Ideology and Ideological State Apparatuses" Dr. Mary Klages, Associate Professor of English, University of Colorado, Boulder, November 6, 2001
Althusser's answer starts with the distinction between ideologies and ideology. IDEOLOGIES are specific, historical, and differing; we can talk about various ideologies, such as Christian ideology, democratic ideology, feminist ideology, Marxist ideology, etc. IDEOLOGY, however, is STRUCTURAL. Althusser says that ideology is a structure, and as such is "eternal," i.e. to be studied synchronically; this is why Althusser says (on p. 240) that ideology has no history. He derives this idea of ideology as a structure from the Marxist idea that ideology is part of the superstructure, but he links the structure of ideology to the idea of the unconscious, from Freud and from Lacan.
Because ideology is a structure, its contents will vary, you can fill it up with anything, but its form, like the structure of the unconscious, is always the same. And ideology works "unconsciously." Like language, ideology is a structure/system which we inhabit, which speaks us, but which gives us the illusion that we're in charge, that we freely chose to believe the things we believe, and that we can find lots of reasons why we believe those things. Althusser's first premise or thesis (p. 241a, in italics) is that "Ideology is a 'representation' of the Imaginary Relationship of Individuals to their Real conditions of existence." He begins his explanation of this pronouncement by looking at why people need this imaginary relation to real conditions of existence. Why not just understand the real?(p. 241b).
One way to get a handle on his work is to realize that Bourdieu was interested in explaining social stratification, and the hierarchy of social values, in contemporary capitalist societies. He wanted to study systems of domination in a way that held some room for social agency but without a notion of complete individual freedom. Bourdieu often evoked Althusser as an example of a theorist who had too mechanical a view of internalized domination, while Sartre represented the opposite extreme of a philosopher who posited free will. Bourdieu believed that we are all constrained by our internalized dispositions (our habitus), deriving from the milieu in which we are socialized, which influence our world view, values, expectations for the future, and tastes. These attributes are part of the symbolic or cultural capital of a social group.