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Modern Monetary Theory (MMT)
1990s–· Theory or school
Experts disagreeEconomists or investors genuinely disagree.
A heterodox theory holding that a government issuing its own currency is limited by inflation, not by running out of money.
See it on the Money & Finance map →How it works
Developed from the 1990s by investor Warren Mosler and economists L. Randall Wray and Stephanie Kelton, MMT says a country that borrows in its own fiat currency cannot be forced to default, since it can always create more. Taxes, in this view, give the currency value and cool inflation rather than fund spending. The real limit is labor, materials and capacity: spend beyond them and prices rise. Many proponents add a federal job guarantee. Kelton's The Deficit Myth (2020) popularized it.
Why it matters
It reframed deficit debates around inflation rather than debt totals, and drew attention as US deficits ran near $2 trillion a year.
Facts, rules and data
In a 2019 Chicago Booth survey of leading economists, none agreed that countries borrowing in their own currency need not worry about deficits. The 2021–22 inflation became a contested test case.
Debates and risks
Whether Congress could raise taxes or cut spending fast enough to stop inflation, as MMT requires, and whether bond markets would stay calm meanwhile, is unproven.
Connections (3)
▸Modern Monetary Theory (MMT) builds its case on Fiat money: currency backed by law and trust, not metalExperts disagree
The connection
MMT's key claims depend on fiat money. Because the dollar is not convertible into gold, and Washington borrows only in dollars, MMT argues the US can never run out of money, only into inflation. Under a gold standard, or for countries borrowing in a currency they do not issue, such as euro members, the argument fails.
When and why
Since Nixon ended dollar–gold convertibility in 1971; MMT writers from Warren Mosler (1993) onward build on Georg Knapp's 1905 'state theory' that money is a creature of law.
How solid is the link?
MMT texts make the link explicit; mainstream economists agree a fiat issuer need not default in its own currency, and dispute what follows from that.
Debates and risks
Whether the argument underrates inflation risk and bond-market limits, shown when UK gilt yields spiked in the 2022 budget crisis, is the core dispute.
▸Modern Monetary Theory (MMT) downplays the danger of The national debt and federal deficitsExperts disagree
The connection
MMT argues a country borrowing in its own currency cannot be forced to default, so the debt total matters less than inflation. Federal debt, in this view, is simply the private sector's savings held as safe dollar assets, and interest rates are a policy choice. Most economists reject this, citing interest costs, bond-market limits and inflation risk.
When and why
Developed from the 1990s by Warren Mosler, L. Randall Wray and others; Stephanie Kelton's 2020 book The Deficit Myth popularized it during record pandemic deficits.
How solid is the link?
This is a debated theoretical claim, not a measured link. Supporters cite Japan's debt above 200% of GDP with low rates; critics cite the 2021–22 inflation.
Debates and risks
Whether Congress would actually raise taxes fast enough to curb inflation, as MMT assumes, and where the real limit on debt lies, are unresolved.
▸Modern Monetary Theory (MMT) leans heavily on Sectoral balances: one sector's deficit is another's surplusFact, law or data
The connection
MMT economists such as Stephanie Kelton and L. Randall Wray use Godley's identity to argue that government deficits are the private sector's surplus: cutting deficits, with trade unchanged, forces households and firms to save less or borrow more. Mainstream economists accept the identity but reject MMT's conclusions about how large deficits can safely be.
When and why
At the Levy Economics Institute and the University of Missouri–Kansas City from the 1990s; popularized by Kelton's The Deficit Myth (2020).
How we know
MMT texts explicitly build on Godley's framework, and Godley worked alongside MMT economists at the Levy Institute.
Debates and risks
Everyone accepts the identity; whether it justifies bigger deficits depends on inflation and interest-rate effects, which are disputed.