An ideology is a set of ideas that constitute one's goals, expectations, and actions. An ideology can be thought of as a comprehensive vision, as a way of looking at things, as in several philosophical tendencies, or a set of ideas proposed by the dominant class of a society to all members of this society. The main purpose behind an ideology is to offer either change in society, or adherence to a set of ideals where conformity already exists, through a normative thought process. Ideologies are systems of abstract thought applied to public matters and thus make this concept central to politics.
In the Marxist account of ideology, it serves as an instrument of social reproduction. In the Marxist economic base and superstructure model of society, base denotes the relations of production, and superstructure denotes the dominant ideology (religious, legal, political systems). The economic base of production determines the political superstructure of a society. Ruling class-interests determine the superstructure and the nature of the justifying ideology—actions feasible because the ruling class control the means of production. Similarly, Louis Althusser proposed a materialistic conception of ideology using the concept of the ideological state apparatus. For Althusser, beliefs and ideas are the products of social practices, not the reverse. What is ultimately important for Althusser are not the subjective beliefs held in the "minds" of human individuals, but rather the material institutions, rituals, and discourses that produce these beliefs.
Many political parties base their political action and program on an ideology. A political ideology is a certain ethical set of ideals, principles, doctrines, myths, or symbols of a social movement, institution, class, or large group that explains how society should work and offers some political and cultural blueprint for a certain social order. A political ideology largely concerns itself with how to allocate power and to what ends it should be used. Some parties follow a certain ideology very closely, while others may take broad inspiration from a group of related ideologies without specifically embracing any one of them.