Endogenous money is an economy’s supply of money that is determined endogenously—that is, as a result of the interactions of other economic variables, rather than exogenously (autonomously) by an external authority such as a central bank. The theoretical basis of this position is that money comes into existence through the requirements of the real economy and that the banking system reserves expand or contract as needed to accommodate loan demand at prevailing interest rates. Central banks implement policy primarily through controlling short-term interest rates. The money supply then adapts to the changes in demand for reserves and credit caused by the interest rate change. The supply curve shifts to the right when financial intermediaries issue new substitutes for money, reacting to profit opportunities during the cycle. Theories of endogenous money date to the 19th century, with the work of Knut Wicksell, and later Joseph Schumpeter. Early versions of this theory appear in Adam Smith's 1776 book The Wealth of Nations. With the existence of credit money, Wicksell argued, two interest rates prevail: the "natural" rate and the "money" rate. The natural rate is the return on capital—or the real profit rate. It can be roughly considered to be equivalent to the marginal product of new capital. The money rate, in turn, is the loan rate, an entirely financial construction. Credit, then, is perceived quite appropriately as "money". Banks provide credit by creating deposits upon which borrowers can draw. Since deposits constitute part of real money balances, therefore the bank can, in essence, "create" money. For Wicksell, the endogenous creation of money, and how it leads to changes in the real market is fundamentally a breakdown of the classical dichotomy between the monetary and real sectors. Money is not a "veil" - agents do react to it and this is not due to some irrational money illusion. However, for Wicksell, in the long run, the quantity theory still holds: money is still neutral in the long run.