In a Money Economy, the Actual or Money Rate of Interest May Differ from the Equilibrium or Natural Rate

Put concisely,Wicksell’s theory is as follows: If it were not for monetary disturbances, the rate of interest would be determined so as to equalize the demand for and the supply of savings. This equilibrium rate, as I prefer to call it, he christens the natural rate of interest. In a money economy, the actual or money rate of interest (“Geldzins”) may differ from the equilibrium or natural rate, because the demand for and the supply of capital do not meet in their natural form but in the form of money, the quantity of which available for capital purposes may be arbitrarily changed by the banks.

--Friedrich A. Hayek, "Theories of the Influence of Money on Prices," in Prices and Production and Other Works: F.A. Hayek on Money, the Business Cycle, and the Gold Standard, ed. Joseph T. Salerno (Auburn, AL: Ludwig von Mises Institute, 2008), 215.