Steve_American wrote:https://www.investopedia.com/insights/what-is-the-quantity-theory-of-money/#:~:text=According%20to%20the%20quantity%20theory%20of%20money%2C%20if%20the%20amount,price%20levels%20will%20also%20double.&text=This%20increase%20in%20price%20levels,and%20services%20in%20an%20economy.
INVESTOPEDIA, What Is the Quantity Theory of Money?
It seems at least some economsts do define 'inflation' as an increse in the money supply.
At least in that an increase in the money supply always leads to inflation.
Your statement is categorically false, and the passage you quoted does not say what you claim it does.
Inflation is an increase in prices.
Deflation is a decrease in prices.
Currency appreciation is an increase in the value of a currency.
Currency depreciation is a decrease in the value of a currency.
An increase in the money supply is an increase in the money supply.
There are proposed and supposed correlations between these things, but you can't substitute definitions based on proposed causal relationships.
The quantity theory of money is descended from the Currency School. Its contemporary, the Banking School argued, more correctly, against the one-to-one ratio proposed by the quantity theory, as quoted by you.
The banking school correctly pointed out, for example, that there is both hording of money, and alternatives to money (barter, basically, which includes hanging a 'will work for food' sign), which preclude a one-to-one correlation (while not denying that such correlations exist (though not as an iron rule--more as a highly probable occurrence)).
I wish you would stop thinking that reading MMT blogs supplied you with a thorough economics education. You could always, you know, actually study economics.