 Both Madison and Rousseau, like most political thinkers of the period, are influenced by Baron de Montesquieu’s The Spirit of the Laws (1748), which is one of the founding texts of modern political theory. Though Montesquieu’s treatise belongs to the tradition of liberalism in political theory, given his scientific approach to social, legal and political systems, his influence extends beyond this tradition. Montesquieu argues that the system of legislation for a people varies appropriately with the particular circumstances of the people. He provides specific analysis of how climate, fertility of the soil, population size, et cetera, affect legislation. He famously distinguishes three main forms of governments: republics (which can either be democratic or aristocratic), monarchies and despotisms. He describes leading characteristics of each. His argument that functional democracies require the population to possess civic virtue in high measure, a virtue that consists in valuing public good above private interest, influences later Enlightenment theorists, including both Rousseau and Madison. He describes the threat of factions to which Madison and Rousseau respond in different (indeed opposite) ways. He provides the basic structure and justification for the balance of political powers that Madison later incorporates into the U.S. Constitution.