" Marx defines the commodity form of circulation (commodity—money —commodity, or C—M—C, for short) as an exchange of use values (the use of shoes against bread, for example) which depends essentially upon the qualities of the goods being exchanged. Money functions here as a convenient intermediary. We now encounter a form of circulation, M—C—M, which begins and ends with exactly the same commodity. The only possible motivation for putting money into circulation on a repeated basis is to obtain more of it at the end than was possessed at the beginning. A quantitative relation replaces the exchange of qualities. Money is thrown into circulation to make more money — a profit. And money that circulates in this way is called capital. "

― David Harvey , The Limits to Capital