Inflation.

(1) The best way to destroy the capitalist system is to debauch the currency. By a continuing process of inflation, governments can confiscate, secretly and unobserved, an important part of the wealth of their citizens.
-John Maynard Keynes

(2) Inflation is the one form of taxation that can be imposed without legislation.
-Milton Friedman

(3) Inflation is thought of as a cruel, and maybe the cruelest, tax because it hits in a many-sectored way, in an unplanned way, and it hits the people on a fixed income hardest.
-Paul A. Volcker