This article examines Aristotle’s theory of ‘factional conflict’ (stasis) in Book 5 of the Politics and claims that it is mainly directed against the a-historical account of constitutional change Plato develops in the Republic. Aristotle’s investigation of the causes of stasis is oriented towards the normative political goal of stabilizing political orders and preventing their ‘change’ (metabolê) into different ones. This article argues that the constitution Aristotle calls ‘polity’ (politeia) constitutes his (...) solution to the challenge of stabilizing democracies and oligarchies. The paper also aims at elucidating Aristotle’s conception of an empirical political science, his political realism, and the method he applies in conjunction with it in the ‘empirical’ Books of the Politics (Book 4 through 6). (shrink)