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. Karl Marx considered capitalism to be a historically specific mode of production (the way in which the productive property is owned and controlled, combined with the corresponding social relations between individuals based on their connection with the process of production). For Marx, the capitalist stage of development or "bourgeois society" represented the most advanced form of social organization to date, but he also thought that the working classes would come to power in a worldwide socialist or communist transformation of human society as the end of the series of first aristocratic, then capitalist and finally working class rule was reached. Following Adam Smith, Marx distinguished the use value of commodities from their exchange value in the market. According to Marx, capital is created with the purchase of commodities for the purpose of creating new commodities with an exchange value higher than the sum of the original purchases. For Marx, the use of labor power had itself become a commodity under capitalism because the exchange value of labor power—as reflected in the wage—is less than the value it produces for the capitalist. He argues this difference in values constitutes surplus value, which the capitalists extract and accumulate. In his book "", Marx argues that the capitalist mode of production is distinguished by how the owners of capital extract this surplus from workers—all prior class societies had extracted surplus labor, but capitalism was new in doing so via the sale-value of produced commodities. He argues that a core requirement of a capitalist society is that a large portion of the population must not possess sources of self-sustenance that would allow them to be independent and must instead be compelled to survive to sell their labor for a living wage. In conjunction with his criticism of capitalism was Marx's belief that exploited labor would be the driving force behind a revolution to a socialist-style economy. For Marx, this cycle of the extraction of the surplus value by the owners of capital or the bourgeoisie becomes the basis of class struggle. This argument is intertwined with Marx's version of the labor theory of value asserting that labor is the source of all value and thus of profit.