On the Principles of Political Economy and Taxation (1817) is a book by David Ricardo on economics. The book concludes that land rent grows as population increases. It also clearly lays out the theory of comparative advantage, which shows that all nations can benefit from free trade, even if a nation lacks an absolute advantage in all sectors of its economy. Ricardo claims in the preface that Turgot, Stuart, Adam Smith, Jean-Baptiste Say, Sismondi, and others had not written enough "satisfactory information" on the topics of rent, profit, and wages. Principles of Political Economy is ostensibly Ricardo's effort to fill that gap in the literature. Regardless of whether the book achieved that goal, it secured, according to Ronald Max Hartwell, Ricardo's position among the great classical economists Smith, Thomas Robert Malthus, John Stuart Mill, and Karl Heinrich Marx.