Technological advances, demographic shifts and persistently lower interest rates have further altered the global economy. Mohamed A. El-Erian, chief economic adviser at the financial firm Allianz, wrote in an email that “modern monetary theory has merit in stimulating debate” on whether those changes provide “for governments to run larger economically sustainable deficits than was previously thought possible.”

Besides the risk of government deficits, M.M.T. throws out a drawerful of other venerable assumptions with Marie Kondo-esque ruthlessness. To start, it instructs you to erase that textbook drawing of a white-haired Uncle Sam collecting tax dollars from the public and then using them to pay for military weapons, highway repairs, federal workers’ wages and more.

Tax revenues are not what finance the government’s expenditures, argues Stephanie Kelton, an economist at Stony Brook University and one of the most influential modern monetary theorists. What actually happens in a country that controls its own currency, she says, is that the government first decides what it’s going to spend. In the United States, Congress agrees on a budget. Then government agencies start handing out dollars to the public to pay for those tanks, earth movers and salaries. Afterward, it takes a portion back in the form of taxes. If the government takes back less than it gave out, there will be a deficit.

“The national debt is nothing more than a historical record of all of the dollars that were spent into the economy and not taxed back, and are currently being saved in the form of Treasury securities,” Ms. Kelton said.

Ms. Kelton, a frequent speaker at business and financial conferences and the chief economic adviser to Mr. Sanders during his 2016 presidential campaign, points out that every dollar the government spends translates into a dollar of income for someone else. So a deficit in the public sector simultaneously produces a surplus outside the government.

The reverse is also true, Ms. Kelton maintains, and that can lead to trouble. The seven biggest American depressions or downturns going back 200 years, she said, were all preceded by government surpluses.