Now we must ask what causes security Prices to fluctuate so that speculative money balances can develop.Fluctuations in the market rate of interest.When the market rate of interest rises,security prices rise.This is because current market value is determined by discounting the future interest payments earned on a security by the market rate of interest.The technical relation between the current market price of a security and the market rate of interest,i,is given by the present value formula.
The formula confirms the principle that market price is inversely related to the market rate of interest.The rate of interest,i,appears in the denominators in the right-hand side of the equation,and the larger the denominators,the smaller the sum of the terms on the right-hand side.Generalizing,security prices vary inversely with the market rate of interest.
ฺBut we are begging the question.Saying that security prices fluctuate in the opposite direction from fluctuations in the interest rate does not explain what causes the fluctuations.What we are
really after is how the market rate of interest is determined.The short answer is: by the interaction of the supply of and demand for money.But this gets us ahead of ourselves because we have not yet finished analyzing the demand foe money.The astute reader will recognize that we have a problem of simultaneous equations.The supply of money,the demand for money,and the price of money(the rate of interest)are mutually interdependent.Thus,for now,we shall have to take the interest rate as a given in analyzing the demand for money.Later,we will see how demand interacts with supply to determine the interest rate.