Book excerpt: Twenty-three centuries after its compilation, 'The Politics' still has much to contribute to this central question of political science. Aristotle's thorough and carefully argued analysis is based on a study of over 150 city constitutions, covering a huge range of political issues in order to establish which types of constitution are best - both ideally and in particular circumstances - and how they may be maintained. Aristotle's opinions form an essential background to the thinking of philosophers such as Thomas Aquinas, Machiavelli and Jean Bodin and both his premises and arguments raise questions that are as relevant to modern society as they were to the ancient world.