Marxist theory is a collection of theories of Karl Marx and his followers, and its application to the study of society, history, economics and politics. Marx rejected the philosophy of classical political economy of the Scottish Enlightenment and its followers, and was influenced by Hegelian philosophy, specifically in terms of its philosophy of history, though he also drew heavily on a number of other philosophers of his time. According to one prominent Marxist philosopher, G. A. Cohen, the Marxist philosopher of history, Karl Korsch, considered Marx to have been "the foremost theorist of the dialectic". Marx's most influential writings include his work Capital: Critique of Political Economy, a critique of capitalism, and his later work, Grundrisse, a critique of classical political economy.
Among Marx's most important economic concepts were the concept of surplus-value and its relationship to the concept of class, as well as the concept of the rate of exploitation. According to Marx, workers produce more than the value of their wages, and Marx's concept of surplus-value is a measure of how much that surplus-value is over and above what is paid to the workers. The difference between this and the ordinary profit is known as surplus-value. The rate of surplus-value is a measure of the ratio of surplus-value to wages and can be seen as the rate of exploitation of workers. Other economic concepts of Marx are the concept of absolute surplus-value, the law of the tendential fall in the rate of profit, and the accumulation of capital.
In his work, "A Short History of the Paradoxes of Exchange Value", published in the International Review of Social History in 1993, Jacques Le Goff explained that Marx did not invent the concept of surplus-value. According to the International Review of Social History, Marx borrowed the idea of surplus-value from "the classical economists (Adam Smith, Ricardo, and Malthus) and the economists of the French classical school (L. Walras, J. Saint-Simon)." In his book The Economic System of Imperial Germany (1885), Walras stated that "… the total amount of the products of society equals the sum of its individual members." But "the individual members do not consume all of this sum; they retain a part of their product". This part of the product is surplus-value, which Walras defines as "the aggregate of wages, interest and profit." Since the early classical economists, the concept of surplus-value was known.