Through the medium of money, men continually exchange the most varied commodities and services. A ceaseless buying and selling, an uninterrupted series of exchanges of things, and labour power--this constitutes the essential part of human relations in capitalistic society. An economic map of these relations, graphically displayed, would not be less confusing than an astronomical map which exhibited the manifold and intersected orbits of the heavenly bodies. And yet there must be some rule or law which operates in this seeming medley of movements; for men do not work or exchange their goods by hazard, like savages who give their entire lumps of gold or rough diamonds for a necklace of glass pearls. The English and French economists in the seventeenth, eighteenth, and nineteenth centuries, amongst whom Petty (1623-87), Quesnay (1694-1759), Adam Smith (1723-96), and Ricardo (1772-1823) were the most original, sought for the laws which regulated exchange operations, and their theories were designated by Marx as classical bourgeois economy. Following up their investigations, Marx declared: Every commodity, that is, every thing or good produced under Capitalism and brought to the market possesses a use value and an exchange value. The use value is the utility of the commodity to satisfy a physical or mental need of its user: a commodity without use value is not exchangeable or saleable. As use values, commodities are materially different from each other; nobody will exchange a ton of wheat for a ton of wheat of the same kind, but he will for clothes. In what measure will commodities exchange with one another? The measure is the exchange value, and this consists in the trouble and quantity of labour which the production of a commodity costs. Equal quantities of labour are exchanged with each other on the market. As exchange values, as the embodiment of human labour, commodities are essentially equal to each other, only quantitatively are they different, as different categories of commodities embody different quantities of labour. It is obvious that the quantities of labour will not be calculated according to the working methods of the individual producers, but according to the prevailing social working methods. If, for example, hand-weaver A requires twenty hours for the production of a piece of cloth, which in a modern factory will be produced in five hours, the cloth of the hand-weaver does not therefore possess four-fold exchange value. If hand-weaver A demands of consumer B an equivalent of twenty working hours, B answers that a similar piece of cloth can be produced in five hours, and therefore it only represents an exchange value of five working hours. Thus, according to Marx, the exchange value of a commodity consists in the quantity of socially necessary labour power which its reproduction would require.