The eurozone is in a bind. Despite successive doses of monetary stimulus by the European Central Bank, inflation remains stubbornly below target. Conventional monetary policy and even quantitative easing evidently have limited potency when interest rates are at or near zero.

Monetary sceptics worry, moreover, that lowering rates further will damage Europe’s banks. Additional asset purchases beyond the monthly level of €20bn ($22bn) already agreed, they warn, will impair the liquidity of financial markets. By pushing up asset prices, the ECB could expose the financial system to stability risks when those lofty prices return to earth.