William Thompson (philosopher) in the context of "Surplus value"

In Marxian economics, surplus value is the difference between the amount raised through a sale of a product and the amount it cost to manufacture it: i.e. the amount raised through sale of the product minus the cost of the materials, plant and labour power. The concept originated in Ricardian socialism, with the term "surplus value" itself being coined by William Thompson in 1824; however, it was not consistently distinguished from the related concepts of surplus labor and surplus product. The concept was subsequently developed and popularized by Karl Marx. Marx's formulation is the standard sense and the primary basis for further developments, though how much of Marx's concept is original and distinct from the Ricardian concept is disputed (see § Origin). Marx's term is the German word "Mehrwert", which simply means value added (sales revenue minus the cost of materials used up), and is cognate to English "more worth".

It is a major concept in Karl Marx's critique of political economy, and, like all of Marx's economic theories, lies outside the economic mainstream. Conventionally, value-added is equal to the sum of gross wage income and gross profit income. However, Marx uses the term Mehrwert to describe the yield, profit or return on production capital invested, i.e. the amount of the increase in the value of capital. Hence, Marx's use of Mehrwert has always been translated as "surplus value", distinguishing it from "value-added". According to Marx's theory, surplus value is equal to the new value created by workers in excess of their own labor-cost, which is appropriated by the capitalist as profit when products are sold. Marx thought that the gigantic increase in wealth and population from the 19th century onwards was mainly due to the competitive striving to obtain maximum surplus-value from the employment of labor, resulting in an equally gigantic increase of productivity and capital resources. To the extent that increasingly the economic surplus is convertible into money and expressed in money, the amassment of wealth is possible on a larger and larger scale (see capital accumulation and surplus product). The concept is closely connected to producer surplus.