Complex sentence: Market monetarists further claim that fiat money central banks have never been unable to boost nominal spending, which would imply that the bank was unable to raise the rate of inflation--that is, to "debase the currency," which it can always do.
Split into simpler sentences: Market monetarists further claim that fiat money central banks have never been unable to boost nominal spending. That would logically imply that the bank was unable to raise the rate of inflation--that is, to "debase the currency," which it can always do.