This essay explores the range of phenomena that can be explained by application of a suitably broad but contentful concept of ideology. According to this concept, an ideology is an evaluative map of the social world, typically featuring an ingroup-outgroup distinction, at least in the case of political ideologies. This concept allows for ideologies that support the existing order and those that challenge it, including revolutionary ideologies. I refute the claim that the concept of ideology is not needed because “voluntary servitude” can be explained as a failure of collective action. I show that ideologies can inhibit revolutionary action as well as stimulate and guide it. They can inhibit revolutionary action by convincing the oppressed that their predicament is natural or inevitable or that they are not being oppressed. They can stimulate and guide revolution by debunking oppression-supporting ideologies and by supplying moral motivation that avoids the calculation of costs and benefits that cause failures of collective action.
