Opposed to the quantity theory of money is the cost of production theory, according to which the value of money depends upon the cost of producing it, rather than upon the supply of it and the demand for it. In general, we may say that the value of any commodity, whether wheat or shoes or gold coin, depends upon the demand for and the supply of the commodity, and in the case of most commodities the supply is limited by the cost of production. There is, therefore, no essential difference between the cost of production theory when properly understood and a reasonable statement of the quantity theory. It must be understood, however, that the cost of production of money affects the level of prices of commodities only through limiting the supply of money. Viewed in this light the cost of production theory harmonizes with the quantity theory. In fact it needs the quantity theory to complete its explanation.