In essence and critically understood, ideology refers to beliefs or a set of beliefs which rationalize, justify, and sanctify vested interests of an individual or a group. (Berger) They rationalize these vested interests by making actions seem to be something different than they are. They justify by providing premises or conclusions which seem to support the interests. They sanctify by making them seem natural or inevitable.
But what are these "vested interests"? They are the activities (i.e. social relations) in which people engage at particular times and in particular places. They are activities IN NEED OF rationalization, justification,and sanctification...can we not presuppose that? They are activities which cannot be presented "on their own"...lest they be seen for what they are...vested interests...rather than defensible standards.
Thus, the really crucial aspect of ideology and ideological thinking is that these ideas/beliefs are INVERTED ideas...the opposite of what the activities really are. When a capitalist business tells us they are doing it all for us...that's an ideological inversion of their profit-making purposes. When a government tells us they make weapons for defense, that's an inversion of their war-making capacities. When an organization tells us they have rules and regulations for "our" convenience, that's an inversion of their bureaucratic and self-perpetuating existence. The understanding of the inverted nature or quality of ideology makes it a TOOL for critical sociological analysis. The first step in this analysis is therefore, to consider the idea in its opposite form and to assess the activity in this light. Where there are discrepancies...you will find rationalization, justification, and sanctification.
One final aspect of ideological thinking is that these ideas are NOT lies. Ideological thinkers aren't lying, they really believe their ideas and are very sincere about maintaining them. Religious ideology is a prime example, as is our belief in democracy in America and of course, capitalism. However, once they are exposed as ideologically-premised, to maintain them is to become a liar. A liar knows the difference, ideological thinkers don't.