1899 in The Distribution of Wealth. The same theorem was formulated later independently by John Atkinson Hobson (1891) and Philip Wicksteed (1894). The political message of this theorem is: "[W]hat a social class gets is, under natural law, what it contributes to the general output of industry." Clark's conclusion rests upon the productive contribution of the last unit of physical labour – one hour unqualified labour – and the last unit of physical capital. To him heterogeneous capital goods have a second, a social form as homogeneous capital (called jelly as a street can be moulded into an engine) and the productivity of the last unit of jelly determines profit. This retakes Karl Marx's view that commodities have a heterogeneous natural form (Naturalform) and also opposed to it a homogenous value-form (Wertform), jelly. Clark might have known this Marxian construction from his German time and was reproached for this similarity. Clark's capital are not produced means of production each with a different production structure. It is an abstract, always existing and never perishing one great tool in the hand of working humanity similar to a field or a waterfall, also considered capital by Clark. The arguable sides of Clark's notion of capital helped to give rise to the Cambridge capital controversy from 1954 to 1965 between the departments of economics at Cambridge University, England, and at MIT in Cambridge, Massachusetts. Paul A. Samuelson's classic 1947 textbook, Economics, disseminated Clark's concept of capital worldwide. Clark was the father of economist John Maurice Clark. Major works The Philosophy of Wealth: Economic Principles Newly Formulated (1886). Capital and Its Earnings (1888). The Distribution of Wealth: A Theory of Wages, Interest and Profits (1899). Essentials of Economic Theory (1907). Social Justice without Socialism (1914). See also Marginal productivity theory John Bates Clark Medal References Further reading Hollander, Jacob H. (1927). "John Bates Clark as an Economist." In: Economic Essays. New York: The Macmillan Company, pp. 1–5. Messori, L. and Orsini, R., "A Biographical Note on John Bates Clark," History of Economic Thought and Policy, 2/2016, pp. 132–140. Messori, L. and Orsini, R., "John Bates Clark: the first American marginalist as a social economist", History of Economic Thought and Policy, 2/2018, pp. 33–53. External links Works by John Bates Clark, at JSTOR Works by John Bates Clark, at Hathi Trust New School: John Bates Clark, 1847–1938 1847 births 1938 deaths Amherst College alumni Columbia University