Backward- versus Forward-Looking Feedback Interest Rate Rules.

This paper proposes conditions for the existence and uniqueness of solutions to systems of differential equations with delays or advances in which some variables are non-predetermined. An application to the issue of optimal interest rate policy is then develop in a flexible-price model where money enters the utility function. Central banks have the choice between a rule that depends on past inflation rates or one that depends on predicted interest rates. When inflation rates are selected over a bounded time interval, the problem is characterized by a system of delay or advanced differential equations. We then prove that if the central bank's forecast horizon is not too long, an active and forward-looking monetary policy is not too destabilizing : the equilibrium trajectory is unique and monotonic.