Inflation is an increase in the quantity of money without a corresponding increase in the demand for money, i.e., for cash holdings. Ludwig von Mises
The use of quantity of money as a target has not been a success. I'm not sure that I would as of today push it as hard as I once did. Milton Friedman
Inflation is always and everywhere a monetary phenomenon in the sense that it is and can be produced only by a more rapid increase in the quantity of money than in output. Milton Friedman