Adam Smith homely observations, making them feel comfortable all along." Classical economists presented competing theories of those of Smith, termed the "labour theory of value". Later Marxian economics descending from classical economics also use Smith's labour theories, in part. The first volume of Karl Marx's major work, "Das Kapital", was published in German in 1867. In it, Marx focused on the labour theory of value and what he considered to be the exploitation of labour by capital. The labour theory of value held that the value of a thing was determined by the labour that went into its production. This contrasts with
Karl Marx value advocated by David Ricardo. The work was enthusiastically received, and the edition sold out quickly. The successful sales of "A Contribution to the Critique of Political Economy" stimulated Marx in the early 1860s to finish work on the three large volumes that would compose his major life's work – "Das Kapital" and the "Theories of Surplus Value", which discussed the theoreticians of political economy, particularly Adam Smith and David Ricardo. "Theories of Surplus Value" is often referred to as the fourth volume of "Das Kapital" and constitutes one of the first comprehensive treatises on the history of economic thought.