While these models can be instructive, today I am going to focus on a weaker standard. Whatever the long-term optimal level of government debt, and whatever the optimal level of external debt, one can separately ask whether either debt level is becoming a more, or less, important economic factor over time.
For government debt, this weaker standard, or stability condition, determines merely whether the ratio of debt to gross domestic product (GDP) is stable. If it is, interest payments on the debt will, in equilibrium, also settle down to a stable proportion of GDP.