One of money's functions is to serve as a “store of value,” meaning that its buying power should remain constant over time. That doesn't imply that prices cannot change as new features are added to goods and services or that their desirability might change with consumer preferences causing a change in price. What it does mean is that money itself should not lose value — that barring events such as those just mentioned, prices should remain stable.
It doesn't take much to realize that this is not what happens. The dollar has been losing value for over one hundred years, ever since the creation of the Federal Reserve Bank. What cost a dollar back then, today costs between $50.00 and $100.00. As a result, holding dollars is a terrible investment. More on page two.