The individual in question behaves in such and such a way, adopts such and such a practical attitude, and, what is more, participates in certain regular practices which are those of the ideological apparatus on which “depend” the ideas which he has in all consciousness freely chosen as a subject. If he believes in God, he goes to church to attend Mass, kneels, prays, confesses, does penance (once it was material in the ordinary sense of the term) and naturally repents and so on. If he believes in Duty, he will have the corresponding attitudes, inscribed in ritual practice, “according to the correct principles.” If he believes in Justice, he will submit unconditionally to the rules of the Law, and may even protest when they are violated, sign petitions, take part in a demonstration, etc.

From Althusser, “Ideology and Ideological State Apparatuses,” NA 1501