how the exchange of goods, or a market, would create incentives to act in the general interest, became the basis of what was then called political economy and later economics. It was also the basis for a theory of law and government that gradually superseded the mercantilist regime then prevalent. Smith asserts that when individuals make a trade they value what they are purchasing more than they value what they are giving in exchange for a commodity. If this were not the case, then they would not make the trade but retain ownership of the more valuable commodity. This notion underlies the concept of mutually-beneficial trade where it is held that both sides tend to benefit by an exchange. Adam Smith is often described as the "father of capitalism" (and the "father of economics"). He described his own preferred economic system as "the system of natural liberty." Smith defined "capital" as stock, and "profit" as the just expectation of retaining the revenue from improvements made to that stock. Smith also viewed capital improvement as being the proper central aim of the economic and political system. Karl Marx A critique of the results of capitalism was formulated by Karl Marx. According to Marx, the treatment of labor as a commodity led to people valuing things more in terms of their price rather than their usefulness (see commodity fetishism), and hence to an expansion of the system of commodities. Much of the history of late capitalism involves what David Harvey called the "system of flexible accumulation" in which more and more things become commodities, the value of which is determined through the process of exchange rather than their use. For example, not only pins are commodities; shares in the ownership of a factory that manufactures pins become commodities; then options on the stock issued in the company that operates the factory become commodities; then portions of the interest rate attached to bonds issued by the company become commodities, and so on. Speculation in these abstract commodities then drives the allocation of materials and labor. Marx believed that the extension of the labor theory of value indicated that owners of productive means would exploit workers by depriving them of the full value that workers themselves create. According to Marx, surplus value is the difference between the value that the worker has created and the wage that the worker receives from his/her employer. Many