In the Classical theory, using the Cambridge approach, the interest rate (the price of money) measures the cost of holding cash. At a given level of k, individuals therefore have what is called ‘loanable funds’ (hence Keynes’ called the Classical Model of interest the ‘Loanable Funds Theory’. Beyond their need for money for transactional purposes, cash can serve as a store of value but yields no return so individuals will tend to hold their excess money in interest yielding securities. The Classical Model assumed that the rational individual would not hold excess money in the form of cash.
Firms borrow funds from individuals in order to build new plant and equipment that eventually will increase Y. However, any investment is associated with a corresponding rate of return. A firm can only earn a profit on a given investment if its rate of return is greater than the opportunity cost of money, i.e. the interest rate. In the Keynsian Model the alternative investment opportunities formed a Marginal Efficiency of Investment Schedule with alternative projects ranked according to their estimated rates of return. Projects with rates above the interest rate would be undertaken while those with rates below the current interest rate would not (Fig. 4.3).
Demand for loanable funds varies inversely with the interest rate. Similarly there is a supply of loanable funds