“Modern Monetary Theory” was coined by Bill Mitchell, an Australian economist and prominent proponent, but its roots are much older. The term is a reference to John Maynard Keynes, the founder of modern macroeconomics. In “A Treatise on Money,” Keynes asserted that “all modern States” have had the ability to decide what is money and what is not for at least 4,000 years.
This claim, that money is a “creature of the state,” is central to the theory. In a “fiat money” system like the one in place in the United States, all money is ultimately created by the government, which prints it and puts it into circulation. Consequently, the thinking goes, the government can never run out of money. It can always make more.
This doesn’t mean that taxes are unnecessary. Taxes, in fact, are key to making the whole system work. The need to pay taxes compels people to use the currency printed by the government. Taxes are also sometimes necessary to prevent the economy from overheating. If consumer demand outpaces the supply of available goods, prices will jump, resulting in inflation (where prices rise even as buying power falls). In this case, taxes can tamp down spending and keep prices low.
But if the theory is correct, there is no reason the amount of money the government takes in needs to match up with the amount it spends. Indeed, its followers call for massive tax cuts and deficit spending during recessions.