yekke2: Consider an economy where one can buy 1 kipa for $1.
Then, due to the government printing money, suppose there are twice as many dollars in the economy. Now, you would think that this is a good thing. In fact, it would be if the population grew and there were more valuable services created. However, in the absence of such modifiers, now $1 is worth half as much as before. So the same kipa now costs $2 instead of $1.
This is what happened in the Weimar Republic after WWI. They owed so much to other countries from the Versailles Treaty that they printed money to pay their debt. As a result, there was hyperinflation, which caused their currency to become virtually worthless. Aside from the economic consequences, the poor state of the economy made way for a young, charasmatic politician named Adolf Hitler Y”S to capture the hearts and minds of the German people. I don’t need to tell you the rest of the story.
Now, I assume you may be asking because of the talk about “quantitative easing.” In a recession with periods of deflation, it is possible to increase the money supply without causing inflation. In the liquidity trap of 2008-2011, the Bank of England pursued quantitative easing (increasing the money supply), but this only had a minimal impact on underlying inflation. This is because although banks saw an increase in their reserves, they were reluctant to increase bank lending.
However, if a Central Bank pursued quantitative easing during a normal period of economic activity like our fictitous economy above, then it would cause inflation.
In the U.S., the question is really about number crunching. The United States is not experiencing deflation, but inflation is virtually 0. So the inflationary results of quantitative easing might not be so drastic.