Fiscal Deficits and National Debt: Modern Monetary Theory, Debt Ceiling Controversy, and Fiscal Sustainability
Government debt is fundamentally different from household debt: households face a genuine burden (must repay from income); for sovereign states with currency-issuing authority, domestic-currency-denominated debt can theoretically always be “money-printed away” (but with inflation as the cost). This fundamental difference produces different frameworks for assessing government debt sustainability.
Modern Monetary Theory’s Core Claims
MMT‘s core claim: sovereign currency nations (able to issue their own currency — US, Japan, but not eurozone member countries) cannot “go bankrupt” on domestic-currency debt because they can create money. The real constraint on fiscal deficits isn’t whether the government can “afford” it (it can always print money), but inflation — government spending exceeding the economy’s actual productive capacity causes inflation. MMT’s policy question: not “how much can the government spend” but “how much idle real economy capacity can government spending activate without causing inflation.”
MMT critics (including mainstream economists like Paul Krugman) argue MMT is too optimistic about inflation constraints, ignoring inflation expectations’ self-fulfilling nature and currency credibility’s fragility. The 2021–2022 US inflation surge is seen by some economists as a real-world test of MMT-adjacent policy (large fiscal stimulus + loose monetary policy).
Japan’s High-Debt, Low-Inflation Puzzle
Japan is the most important case study for high government debt effects: debt/GDP ratio approximately 260% (globally highest), yet facing deflation rather than inflation long-term, with bond yields near zero (or negative). Key explanatory factors: high savings rate (domestic investors hold large government bond quantities), aging population’s insufficient domestic demand, Bank of Japan’s yield curve control (YCC) policy. Japan’s case supports “debt sustainability depends on domestic savings structure, not absolute debt scale” — but some economists warn it’s an unreplicable special case.
