That's not really a good argument though because there are 2 definitions of inflation which are often confused due to the fact that they have the same name, and

That's not really a good argument though because there are 2 definitions of inflation which are often confused due to the fact that they have the same name, and can lead to the same results. One is "the generalized increase in prices" and the other is "The increase of the money supply". If you understand that those 2 things are inflation, but not the same thing, then you can see why there's some issues calling an increase in prices that isn't the result of an increase in the money supply "inflation", and vice versa. This gets worse when you realize that an increase in the money supply can (but is not guaranteed) to cause an increase in prices. Like the professor says "The key driver of inflation is not just how much money exists in the world; it's what are people doing with that money." What he's really saying here is that "The key driver of (general increase in prices) is not just (increase of the money supply) but what are people doing with that (increase of the money supply)". You can have inflation even with a reducing money supply, for example when production decreases, or when velocity of money is higher. In fact this brings me to another point that really irks me, which is that M2 and above are arguably not even money in the first place. They are better described as liquidity, and calling them money simply increases confusion with actual money. By making that distinction clear, this dual definition of inflation becomes clearer since it becomes obvious that an increase in liquidity (willingness and ability to spend) can increase prices, regardless of whether the actual liquid (money) has increased. Just like a pipe, you can pump more stuff out by either increasing pressure (increasing money) or making the pipe have less friction (liquidity).