The systematic study of how political institutions, customs and practices vary across societies and periods, looking for patterns and explanations rather than treating each case in isolation. Its governing assumption is that political arrangements can be explained rather than merely narrated, and that comparison is the closest thing political science has to an experiment.
Aristotle began it by collecting and classifying constitutions, and the method was recovered by Montesquieu, whose Spirit of the Laws (1748) tied political forms to climate, commerce, religion and the size of territory. Tocqueville treated America as a laboratory for understanding democratic society in general rather than as a country worth describing for its own sake, and Weber extended the comparative method across civilizations to ask why bureaucratic rationalization had taken hold where it did.
The field professionalized after the war and has swung between methods since. The behavioral revolution pushed toward survey data and quantification; area specialists objected that statistical work on incomparable cases produces precision without understanding; the historical-institutionalist turn re-established sequence and path dependence as explanations. Its durable findings tend to be conditional rather than lawlike: Lijphart on how consociational arrangements hold divided societies together, Przeworski on the relationship between development and the survival of democracies, Linz on why presidential systems are more fragile than parliamentary ones.
The field's recurring methodological problem is that it has many variables and few cases — there are only so many countries, and they are not independent of one another. Its current work on democratic erosion has made that limitation newly visible, since the cases most worth explaining are still in progress.
