Interest Rates: Which Theory Is Correct?
Reconciling Stocks and Flows
by
Charles Lamson
Liquidity preference is the name given to the theory based on the demand for and supply of money. It was developed by John Maynard Keynes in the 1930s. The supply of money is the stock of money, and the demand for money, or "preference for liquidity," is how much money spending units wish to hold. The supply of and demand for money is partially determined by the central bank, through its control over the stock of reserves and reserve requirements. Also, the demand for money is based on the spending plans of spending units. Demand is related to the interest rate, ceteris paribus (all other things being equal). The interest rate adjusts to equate the quantity supplied (stock) of money with the quantity demanded.
The loanable funds theory is based on flows as opposed to stocks. Flows are measured throughout time, whereas stocks are measured at a point in time. Thus, if I offered you a job for $10,000, you will want to know whether this is per week, per month, or per year. Not so for stocks. If I give you a $10,000 savings account, there is no relevant time dimension. The loanable funds theory develops the argument that the interest rate is determined by the supply of and demand for loanable funds. The demand for loanable funds reflects borrowing plans by DSUs, while the supply of loanable funds reflects lending plans by SSUs. Ceteris paribus, the quantity demanded of loanable funds is inversely related to the interest rate, while the quantity supplied of loanable funds is directly related to the interest rate. The interest rate adjusts to equate the quantity demanded of loanable funds with the quantity supplied.
To help you see that the theories compliment each other, consider what happens when the Fed increases bank reserves. When reserves increase, banks create money by incurring deposit liabilities as they acquire loans. In doing so, banks have simultaneously augmented the supply of loanable funds. According to liquidity preference, an increase in the supply of money, ceteris paribus, causes the interest rate to fall, while according to the loanable funds theory, an increase in the supply of loanable funds have the same effect. Likewise, if the Fed decreases the supply of reserves, you should be able to verify that both the stock of money and the supply of loanable funds decrease, leading to a higher interest rate. Again, both theories predict that interest rate changes in the same direction.
Next consider what happens when the demand for loanable funds increases, reflecting an increased desire of people to borrow more at every interest rate. Since banks acquire loan assets when they create checkable deposits, which are also money, an increase in the demand for loanable funds corresponds to an increase in the demand for money. According to both theories, an increase in the interest rate results. Likewise, a decrease in the demand for loanable funds translate to a decrease in the demand for money and a lower interest rate.
From an intuitive standpoint, we can reconcile the two theories by recognizing that when there is a change in a stock measured at different times, a flow has occurred, that is, a flow over time results in a change in a stock. For example, if I have a gallon of milk in the morning, go to the refrigerator for a glass of milk repeatedly throughout the day, and have a gallon left at the end of the day, then I can safely say that I consumed a half gallon of milk during the day. Consumption of milk over the course of the day represents a flow, while the amount of milk in the refrigerator at a point in time is a stock. The change in the stock of milk as measured at two different points in time depicts the flow. If I save $100 per year, at the end of the year, my stock of wealth will have increased by $100 (ignoring interest payments for the time being). Correspondingly, changes in the supply (flow) of loanable funds entail changes in the stock of money measured at two different points in time. Likewise, changes in the demand (flow) of loanable funds entail changes in the demand for money. A theory stated in flows can always be reformulated in terms of stocks and vice versa.
*SOURCE: THE FINANCIAL SYSTEM & THE ECONOMY, 3RD EDITION, 2003, MAUREEN BURTON & RAY LOMBRA, PGS. 72-73*
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