The popular view today is based on the linear Quantity Theory of Money. It seems to be common sense. If more units of a currency are issued, then the value of each unit should fall. Many people may not think of it in explicit terms, but the idea is that the value of one unit of a currency is 1/N, where N is the total money supply. If you double the money supply, then you halve the value of each currency unit.
Inflation, according to this view, is either the cause -- the increase in the money supply itself. Or it's the effect -- rising prices. The Keynesians hold that inflation is good, and the Monetarists basically agree, though they quibble that the rate should be limited. The Austrians universally think inflation is bad.
The Quantity Theory is not based in reality. One should think of this theory like the Lamarckian theory of evolution. Lamarck asserted that changes to an animal's body -- e.g. its tail is cut off -- can be passed on to its offspring. At the time, this theory may have seemed only common sense, and it was very convenient, if not tempting. The same is true with the Quantity Theory of Money. It is convenient, seems like common sense, tempting -- and wrong.
The Fed has been inflicting Quantitative Easing on us for five years ...