Political ideologies are systems of justification for competing social groups having different interests and incentives for action. The policies of party X, whether advocated or implemented, must be justified in the face of counter-policies from party Y. Party X advocates a line of action as indispensable, while party Y thinks it disastrous. Each contention must be supported by convincing reasons which go to build up an alternative political world picture. As in a scientific theory, an ideology which cannot satisfactorily explain or justify a range of phenomena thought to fall under its jurisdiction is seriously flawed. Its weakness will be probed and exposed by those embracing alternative ideology. In metaphorical terms, ideologies must shield themselves from the thrusts of rivals and, in turn, attack them at their most vulnerable points. As a process, ideological discourse can be seen as a group's never-ending task of expounding new arguments to justify policies in the face of systematic criticism from other discoursing agents. New and more elaborate arguments develop in situations of weakness in the face of alternative, more persuasive views. This unfolding of discourse in response to other discourse is a socio-psychological phenomenon, but epistemological factors, e.g. the perception of contrary statements and fallacious argument, play an important part in deciding the line of development and acceptable discoursive form.

From Greek times, philosophers have recognised the importance of debate in the development of new ideas, and in the pursuit of truth.