shared by David Ricardo, second most important of the classical political economists and one of the most influential economists of modern times. In The Principles of Political Economy and Taxation (1817), Ricardo developed the law of comparative advantage, which explains why it is profitable for two parties to trade, even if one of the trading partners is more efficient in every type of economic production. This principle supports the economic case for free trade. Ricardo was a supporter of Say's law and held the view that full employment is the normal equilibrium for a competitive economy. He also argued that inflation is closely related to changes in quantity of money and credit and was a proponent of the law of diminishing returns, which states that each additional unit of input yields less and less additional output. The values of classical political economy are strongly associated with the classical liberal doctrine of minimal government intervention in the economy, though it does not necessarily oppose the state's provision of a few basic public goods. Classical liberal thought has generally assumed a clear division between the economy and other realms of social activity, such as the state. Marx and critique of political economy Karl Marx considered capitalism to be a historically specific mode of production. Marx's critique of political economy encompasses the study and exposition of the mode of production and ideology of bourgeois society, that is, the fundamental "economic" and social categories present within what for Marx is the capitalist mode of production. In contrast to the classics of political economy, Marx was concerned with lifting the "ideological veil" of surface phenomena and exposing the norms, axioms, social practices, institutions and so on, that reproduced the social phenomenon of capital. The central works in Marx's critique of political economy are Grundrisse, A Contribution to the Critique of Political Economy and Das Kapital. Marx's companion Friedrich Engels also critiqued the economy in his Outlines of a Critique of Political Economy (1844), which helped lay down some foundation for what Marx was to take further, and Engels just like Marx also compared economists with theologians, e.g by referring to Adam Smith as the economic Luther. Some foundational concepts in Marx critique of political economy are the following: Labour and capital are historically specific forms of social relations, and labour isn't the source of all wealth. Labour is the other side of the same coin