But uncertainty about the path of future interest rates (and differences in investor preferences) will make debt of different maturities imperfect substitutes. Because of this, changes in the mix of short-term and long-term bonds offered by the government will change relative prices and thus influence the shape of the yield curve. At the same time, monetary policy based on setting the policy rate becomes less effective: the lower the degree of asset substitutability, the weaker the transmission of changes in the overnight rate to other interest rates. Hence government debt management policies (or central bank purchases of bonds) become more.
