The paper deals with the topic of interest rate, which has long been confused with usury and is
determined by parsimony and the marginal product of capital or, as an alternative, by conventions.
It will be shown how the return differentials and the ever changing relationship that financial
capital establishes with industrial capital are determined, starting from the risk-free rate or
benchmark. As far as the level of the interest rate is concerned, the risks connected with both a
‘‘high’’ and a ‘‘low’’ cost of money are outlined. After having demonstrated how interest rate is,
on the one hand, a policy variable and, on the other, a determinant of investments and the output
gap, it will be shown how his level affects income distribution, the area in which the dialogue between
economics and ethics has been most fertile.