  This paper compares different implementations of monetary policy in a
new-Keynesian setting. We can show that a shift from Ramsey optimal policy
under short-term commitment (based on a negative feedback mechanism) to a
Taylor rule (based on a positive feedback mechanism) corresponds to a Hopf
bifurcation with opposite policy advice and a change of the dynamic properties.
This bifurcation occurs because of the ad hoc assumption that interest rate is
a forward-looking variable when policy targets (inflation and output gap) are
forward-looking variables in the new-Keynesian theory.
