Imagine a simple economy without money and only two goods: Apples and oranges. Now, one apple is worth as much as one orange. If the price of apples rises that means the price of oranges falls. (If the price of an apple is two oranges, the price of an orange is half an apple.)

Thus, if inflation means that everything gets more expensive, there could be no inflation in this simple economy.

Nor does it make any difference if we introduce bananas or infinitely many other goods into the economy.

But what if there was a good that we didn’t ordinarily think of as a good, so that when we say everything gets more expensive we mean everything but that good, everything measured in that good?

This good is money.

When we say everything gets more expensive we could also say money gets cheaper. For 10 dollars you can buy less apples, but for 10 apples you can buy more dollars.

So how does money get cheaper? Like any other good it gets cheaper if its supply is increased, if the central bank (or a counterfeiter) prints money.