Political science is a social science discipline concerned with the study of the state, government, and politics. Aristotle defined it as the study of the state. It deals extensively with the theory and practice of politics, and the analysis of political systems and political behavior. Political scientists "see themselves engaged in revealing the relationships underlying political events and conditions, and from these revelations they attempt to construct general principles about the way the world of politics works." Political science intersects with other fields; including anthropology, public policy, national politics, economics, international relations, comparative politics,  psychology, sociology, history, law, and political theory. Although it was codified in the 19th century, when all the social sciences were established, political science has ancient roots; indeed, it originated almost 2,500 years ago with the works of Plato and Aristotle.