Money: theory and regime across eras
For most of history money was a thing you could bite. Then it became a promise, then a number on a screen. Every time the money changed, the theory of what money is changed with it — and every time the theory changed, it was because the regime had already moved. This is the thread where what people thought money was and how money actually worked kept rewriting each other.
See the money lineage as a graphCommodity money: money is the metal
“The ordinary means therefore to encrease our wealth and treasure is by Forraign Trade, wherein wee must ever observe this rule: to sell more to strangers yearly than wee consume of theirs in value.”
— Thomas Mun, England’s Treasure by Forraign Trade (written 1620s, published 1664)
When Mun wrote “treasure,” he meant metal — actual silver and gold piled in a vault. A nation got rich, in this picture, by piling up specie, and the balance of trade was the pipe through which the metal flowed in or out. This was not a quirk of one writer’s theory. The coins in a purse were the money, and the only monetary lever a sovereign had was the metal content of the coin — which is why, whenever a king ran short of cash, he was tempted to cut the silver and call the lighter coin the same name. Everyone could feel the result in their purse.
Start with the theory the mercantilists actually held, because it is easy to caricature and we should not. Bullionism says money’s value is the metal: a coin is worth what the silver in it is worth, national wealth is the stock of specie a country holds, and the way to accumulate specie is to run a trade surplus so foreigners ship their metal to you. It is a commodity theory of money in the most literal sense — money is a commodity that happens to be useful for exchange. The intellectual lineage runs through the mercantilist writers and the physiocrats who reacted to them; the same chapter carries Hume’s eventual demolition of the doctrine, but hold that — the rebuttal is the next stage.
Now the regime that theory described, because they are the same object seen twice. For two thousand years money was stamped metal. A Roman denarius, a medieval penny, a Spanish piece of eight — each was a weighed lump of silver with a sovereign’s mark certifying the weight and fineness. And here the regime carried its own recurring stress: debasement. A ruler who needed revenue could recall the coinage, melt it, mix in base metal, and reissue more coins of the same face value from the same silver. Rome did it for three centuries — the denarius fell from nearly pure silver under Augustus to about 5% silver by the 260s AD. Medieval mints clipped and reminted; Henry VIII’s “Great Debasement” of the 1540s cut the silver in English coin by two-thirds. Under a metallic regime, debasement was monetary policy — the only one available — and it was both irresistible to the sovereign and destabilizing to everyone holding the old coins.
The mercantilist doctrine and its institutional apparatus — the trade-surplus rule, the specie obsession, and why the discipline eventually rejected it — live in the history of economic thought:
Why bullionism was right about a metallic world
It is fashionable to treat the mercantilists as confused — hoarding shiny metal while mistaking it for wealth. That condescension misreads the regime they lived in. In a world where money is metal, accumulating metal really is accumulating purchasing power, because the metal is the thing every other country will accept. A state that ran out of specie could not pay its soldiers, could not buy grain in a famine, could not import the gunpowder to defend itself — and it could not simply print more, because there was nothing to print. The mercantilist fixation on the trade balance was the rational response to a constraint that genuinely bound: under a metallic regime, the specie stock was the war chest, and a country that let its metal drain away was disarming itself. Bullionism was not a confusion about what wealth is. It was a coherent account of money in a world where money was a scarce commodity you could not manufacture.
Hold that picture as the strongest version, because the critique that undoes it does not come from a cleverer theorist. It comes from inside the regime itself.
Where this leaves us
Money was metal, and bullionism was the right theory of a metallic world — a theory that fit its regime so tightly that thought and practice were indistinguishable. But the regime carried the seed of its own undoing. Every debasement ran the same experiment: cut the silver in the coin, and after a lag, prices rose to match. What the holder cared about turned out not to be the metal but what the coin could buy — and the inflations that followed debasements were the first evidence that money’s value might track its quantity rather than its substance. Bullionism fit the metallic coinage regime exactly; and the regime’s own debasement stress is the raw observation that the next theory rung — the quantity theory — would generalize from a recurring royal swindle into a law of money.
If a king could double the number of coins by halving the silver in each, and prices simply doubled in response, then maybe money’s value was never about the metal at all. A Scottish philosopher writing in 1752 took that hunch and turned it into a self-correcting mechanism — one that would quietly govern the world’s money for the next century and a half.
The veil and the self-regulating standard
“Suppose four-fifths of all the money in Great Britain to be annihilated in one night … what would be the consequence? Must not the price of all labour and commodities sink in proportion? … the same causes, which would correct these exorbitant inequalities, were they to happen miraculously, must prevent their happening in the common course of nature.”
— David Hume, Of the Balance of Trade (1752)
Hume is describing a machine. Money that piles up in one country raises its prices; high prices send buyers abroad; the metal flows out to where prices are lower; and the outflow pulls the price levels back into line — automatically, with no one in charge. He called it the price-specie-flow mechanism, and a century later it was not a thought experiment. It was the literal operating principle of the world’s money: the classical gold standard of the 1870s to 1914, under which every major currency was a fixed weight of gold and the flow of metal between nations did exactly what Hume said it would.
Hume’s mechanism contains a deeper claim, the one that would dominate monetary thought for two centuries: money is a veil. If annihilating four-fifths of the money just lowers every price proportionally and changes nothing real, then the quantity of money sets the price level and nothing else. Double the money, double the prices, leave the actual goods, jobs, and trades untouched. Ricardo carried this from Hume’s open-economy version into a domestic doctrine during Britain’s bullionist controversy of 1810, and the result is the quantity theory of money: the most durable proposition in monetary economics, and the one that made “money is the metal” obsolete by showing that what matters is how much money there is, not what it is made of.
The quantity theory is usually written as the equation of exchange, relating the money stock $M$, the velocity of circulation $V$, the price level $P$, and the volume of real transactions $Q$:
$$MV = PQ$$Hold velocity roughly constant and real output $Q$ pinned by the real economy, and the price level moves one-for-one with the money stock. In growth-rate form, inflation is the money-growth rate minus the real-growth rate:
$$\pi = \mu - g$$Money is neutral in the long run: a change in $M$ shows up entirely in $P$, never in real quantities. The full treatment of money demand and the monetary apparatus is the home for this:
Picture a country with a fixed pile of goods and a fixed number of coins. Now wave a wand and double the coins overnight. Nothing real has changed — same farms, same factories, same hours worked — so the only thing that can give is the price tags. Twice as many coins chasing the same goods, so every price doubles. The coins are a veil draped over a real economy that goes about its business underneath; pull the veil thicker or thinner and the shapes beneath stay the same.
And the regime, again the same object seen twice. The classical gold standard was Hume’s mechanism cast in institutions. Each currency was defined as a fixed weight of gold; the money supply was tethered to the national gold stock; and when a country ran a trade deficit, gold physically left its vaults, contracting its money supply, lowering its prices, and restoring its trade balance — exactly the self-correcting flow Hume had drawn on paper. No committee decided this. The metal decided it. The gold standard, in other words, was the quantity theory made institutional: under it, money really was roughly neutral, $MV=PQ$ really did roughly bind, and the price level really did discipline itself. The theory described the regime because the regime had been built to run on the theory.
The classical gold standard as a working regime — its spread, its rules, its costs — is the spine of the economic-history chapter on the era:
For the intellectual lineage — Hume’s specie-flow argument and Ricardo’s bullionist formalization — the two threads sit one chapter apart: Hume in HET Ch.2 §2.6 (Hume’s specie-flow), where he first turns the mercantilist picture against itself, and Ricardo’s quantity-theory turn in HET Ch.3 §3.6 (the bullionist controversy).
Why money-neutrality looked like a law of nature
Take the quantity-theory-under-gold-standard picture at its full strength, because it earned its authority. The classical gold standard delivered something no monetary regime had managed before and few have managed since: roughly stable prices over the long run across the whole trading world, and a settlement system that let a London merchant and a Buenos Aires exporter transact across an ocean in a currency each trusted. “Sound money” was not an ideology to the Victorians; it was a working machine they could watch operate. And the quantity theory genuinely predicted how that machine behaved — gold discoveries in California and Australia in the 1850s produced the mild inflations the theory said they would; the gold scarcity of the 1870s to 1890s produced the deflation it predicted. When your theory forecasts the price level from the metal supply and keeps being right, treating money-neutrality as close to a law of nature is not dogma. It is induction. The classical economists believed money was a veil because, under their regime, it very nearly was.
Where this leaves us
The quantity theory won the argument against bullionism — what matters is the quantity of money, not its substance — and it was the right theory of its own regime besides. Money was a veil under the gold standard, and the gold standard was the quantity theory made real. But read the verdict carefully, because it is conditional. The neutrality and the self-regulation were properties of the regime, not of money as such; they held because gold convertibility forced the money supply to behave a certain way and forced wages and prices to take the adjustment. The quantity theory was true because the gold standard made it true — and that means when the gold standard broke, the theory’s “law” was going to break with it. For the full chronology of how that regime spread, strained, and finally shattered, see History Ch.11 (the gold standard era).
The gold standard’s self-regulation came with a price: when the metal demanded that a country deflate, it deflated whether the economy could bear it or not. In 1925 Britain went back onto gold at the pre-war parity, and a young Cambridge economist watched the deflation crush British industry and concluded that money was not a veil at all. It was a refuge — the thing people run to when the future stops being trustworthy.
The metallic regime breaks, and theory follows
“Money is a creature of law.”
— Georg Friedrich Knapp, The State Theory of Money (Staatliche Theorie des Geldes, 1905)
In one sentence Knapp inverts two thousand years of common sense. Money is not metal that happens to be useful; money is whatever the state declares it will accept to settle a debt to itself — a creature of law, not of nature. In 1905 this read as a curiosity. Within a generation it read as a description. Britain returned to gold at the pre-war parity in 1925, against Keynes’s public warning, and got mass unemployment for its trouble; sterling fell off gold in 1931, and the metallic order that had run the world unravelled in a cascade of devaluations; and in 1944, at Bretton Woods, the survivors built a deliberately half-metallic compromise — gold-anchored at one remove, but managed by states. The regime that had embodied the quantity theory was coming apart, and theory had to decide what money was once the metal let go.
Two theoretical moves answer the breaking regime, and they couple. The first is chartalism, Knapp’s state theory: money has value not because of any metal in it but because the state demands it back — taxes are denominated in it, debts are enforced in it, and a population that must acquire the state’s token to settle its obligations will accept that token in trade. The second is Keynes’s liquidity preference, the heart of the 1936 General Theory and already sketched in the 1923 Tract on Monetary Reform: money is held not just to transact but as a store of value under uncertainty — a refuge you reach for precisely when the future looks dangerous. That second point is where money stops being neutral. When everyone reaches for the refuge at once, the demand for money is a demand for liquidity itself, and no quantity equation pins the price level, because velocity collapses as money is hoarded rather than spent.
Keynes’s money-demand function makes the desired real money balance depend on income $Y$ (the transactions motive) and inversely on the interest rate $i$ (the opportunity cost of holding money rather than bonds, plus the speculative and precautionary motives):
$$\frac{M^d}{P} = L(Y, i), \qquad \frac{\partial L}{\partial Y} > 0, \quad \frac{\partial L}{\partial i} < 0$$As $i$ falls toward zero, $L$ becomes very flat — the liquidity trap, where people will hold any quantity of money rather than bonds, and adding money no longer lowers rates or stimulates spending. Money demand becomes a bottomless preference for liquidity, and the quantity theory’s tidy link from $M$ to $P$ simply dissolves.
In a panic, everyone wants to hold the one thing that is certain — money — rather than spend it or lend it. That desire is not a footnote to the economy; it is itself a macroeconomic force. When the whole population reaches for cash at the same moment, spending dries up, prices fall, and the “more money means higher prices” rule breaks down completely: you can pour money in and watch it sit there, hoarded, because what people want is not goods but safety.
The regime strand is what made both moves not just possible but credible. The interwar collapse ran the decisive experiment: when Britain suspended gold convertibility in 1931, the pound did not vanish and prices did not stop being quoted in sterling. Money kept working without the metal — which is direct evidence for Knapp’s claim that the state, not the gold, was what made money money. And the Depression itself was Keynes’s evidence: a liquidity trap, not a quantity-theory equilibrium, in which people hoarded cash and no expansion of the money base could force them to spend. The metallic regime’s collapse is precisely what made the chartalist and Keynesian moves necessary and credible — once gold let go and money kept functioning, “money is metal” was empirically dead, and “money is a state liability held under uncertainty” was the only picture the surviving regime actually fit. The full regime history is two chapters: the collapse and the rebuild.
The two theory lineages live in different chapters because they entered the discipline by different doors. Keynes’s liquidity-preference theory is the spine of HET Ch.8 §8.2 (the General Theory). Knapp’s chartalism had no chapter of its own in the mainstream for most of a century — it survived at the edge and resurfaced through Modern Monetary Theory, which is why its home is the modern-pluralism chapter’s frontier section, HET Ch.17 §17.5 (the expanding frontier, including MMT).
Watching the metallist picture fail in real time
Argue both new theories at full strength, because both arrived as honest readings of a falsifying event rather than as intellectual fashions. The chartalist case is almost embarrassingly concrete: in 1931–33, one country after another cut the gold tie, and in every case the national money went on circulating, prices went on being quoted, wages went on being paid — in a token that was now backed by nothing but the state’s word and the state’s tax demand. If money were really the metal, severing the metal should have destroyed the money. It did not. The only account left standing was Knapp’s: what makes a thing money is that the sovereign denominates obligations in it and accepts it back. The metal had been a convenient anchor, never the source of the value.
Keynes’s case is the other half. The classical economists had no room in their theory for a depression that simply would not end — under the quantity theory, falling prices should restore full employment by raising real money balances. Keynes saw what actually happened: prices fell and employment did not recover, because the falling prices fed an expectation of further falls, and people held money rather than spend it. The demand for liquidity became a sink that swallowed every attempt to reflate. This was not a market that needed time to clear. It was a system that could sit at mass unemployment indefinitely because money was a refuge, and in a frightened economy everyone wants the refuge at once. A reader watching 1931 unfold should feel the metallist and quantity-theory picture failing under the weight of events, and the new theories arriving not as cleverness but as the only honest description left.
“Money is a creature of law. A theory of money must therefore deal with legal history.”
— Georg Friedrich Knapp, The State Theory of Money, 1905
Does the state, not the metal, make money money?
Knapp said money is whatever the sovereign accepts to settle a debt to itself. For two thousand years that sounded backwards. Then the gold standard collapsed and money kept working — which is exactly what his theory predicted and the metallist theory could not explain.
Where this leaves us
The metallic regime broke, and theory followed it honestly. Money turned out to be a state liability, held for its liquidity when the future is uncertain — and the chartalist and Keynesian moves were the right reading of a world in which gold no longer disciplined the price level and no longer needed to. The gold standard’s collapse did not merely change the regime; it falsified the metallist theory outright, and forced the theory of money to relocate — from the metal, to the state that demands the token and the expectations that govern whether people spend it or hoard it. For the regime chronology, see History Ch.12 (the collapse) and Ch.13 (the rebuild).
Bretton Woods kept a single thread of gold running through the system — the dollar was still convertible at $35 an ounce, and every other currency hung off the dollar. But by 1971 the thread had pulled taut and snapped, and for the first time in history the entire world’s money was backed by nothing but the state’s word. The question “what is money?” was now wide open — and a Chicago economist had an answer ready.
Fiat, monetarism, and the live frontier
“I have directed Secretary Connally to suspend temporarily the convertibility of the dollar into gold or other reserve assets … to defend the dollar against the speculators.”
— Richard Nixon, televised address, August 15, 1971
“Temporarily” turned out to mean forever. With that announcement the last thread of gold was cut, and for the first time the entire world’s money floated free of metal — backed by nothing but each government’s word and each central bank’s discipline. The question Knapp had posed in 1905 was now the operating condition of the whole planet: if money is not metal, what is it, and what makes it hold its value? Two theory rungs answer the fiat regime in turn — Friedman’s monetarism for the early fiat decades, and the post-2008 argument over credit and state liabilities for the era in which the monetarist machinery stopped working.
Theory rung one: monetarism. Milton Friedman rescued the quantity theory for a metal-free world. His claim — “inflation is always and everywhere a monetary phenomenon” — relocated the discipline that gold used to impose into the hands of the central bank: a fiat currency holds its value if and only if the issuer controls the money supply, and inflation is what happens when the issuer lets the money grow faster than output. The veil survives into the fiat era, but as a policy rule rather than a law of metal. The monetarist lineage is the counter-revolution chapter, HET Ch.10 §10.1 (Friedman’s monetarism).
Theory rung two: credit, endogenous money, and MMT. The other modern rung says the quantity theory had the causation backwards. In a credit economy, money is created when banks lend — loans create deposits, not the reverse — so the money supply is endogenous, pulled into being by demand for credit rather than pushed out by the central bank. Push this to the public sector and you reach Modern Monetary Theory: a state that issues its own currency spends by crediting accounts and is constrained by real resources and inflation, not by a need to “find the money” first. Underneath both sits the old credit-theory lineage — Alfred Mitchell-Innes in 1913, and more recently the anthropology of debt — arguing money was always a ledger of obligations, with the metal a late and incidental settlement device. The MMT and endogenous-money home is the modern-pluralism frontier, HET Ch.17 §17.5.
Distinct from that heterodox rung is the mainstream fiscal-monetary frontier: the fiscal theory of the price level, which says the price level adjusts so that the real value of government debt equals the present value of the surpluses that will service it. It is the New Keynesian consensus’s answer to the same question MMT poses — what backs fiat money — and it belongs to a different chapter, HET Ch.12 §12.3 (inflation targeting and the policy consensus), not to the modern-pluralism frontier above.
The fiscal theory of the price level writes the government’s intertemporal budget constraint as a valuation equation: the real value of nominal debt $B_t$ equals the present discounted value of all future primary surpluses,
$$\frac{B_t}{P_t} = \sum_{s=0}^{\infty} \beta^s \, E_t\!\left[\text{surplus}_{t+s}\right]$$Read as a theory of the price level, $P_t$ is whatever makes this hold: if markets expect smaller future surpluses, $P_t$ rises to inflate away the real debt. Money is backed by the fiscal flows behind it, not by metal. The full apparatus — the government budget constraint, seigniorage, and the FTPL — is in Economics Ch.16 §16.5.
Once the metal is gone, fiat money is an IOU — the only question is whose. When a bank makes a loan and credits your account, the money you now hold is the bank’s IOU. When the government spends and taxes, the dollar in your pocket is the state’s IOU, good because the state will take it back in taxes. The fiscal theory just adds the discipline: the state’s IOU is worth its face value only if there are real surpluses standing behind it — promise to repay with nothing, and the IOU loses value through inflation.
The regime moves in two stages too. Regime rung one: early fiat and Volcker. The 1970s — floating rates, oil shocks, double-digit inflation — looked like Friedman’s vindication: the metal-free dollar lost discipline and inflation ran. Then Paul Volcker’s Federal Reserve crushed it from 1979 to 1982 by brute control of the money supply, at the cost of a deep recession, and monetarism had its policy proof. Regime rung two: QE and the broken multiplier. Then 2008 ran the opposite experiment. The Fed roughly tripled the monetary base through quantitative easing — and inflation barely moved. The money multiplier collapsed; banks held the new reserves rather than lending them; and with interest rates pinned at zero, money demand became nearly flat — Keynes’s liquidity trap, at continental scale. The QE regime broke the monetarist mechanics — and that breakdown is exactly why the live debates over credit, endogenous money, and fiscal backing revived, because the inherited apparatus no longer pinned the price level the way it had under metal or early fiat.
The great-moderation fiat regime that preceded the crisis — the decades when inflation targeting seemed to have solved monetary policy — is the backdrop in History Ch.18; the international side of the fiat regime, the float and the global imbalances it produced, sits in Economics Ch.17 §17.7.
Two modern theories, each right about its regime
Monetarism deserves its due. In the early fiat era it was simply correct: the 1970s inflation was a monetary phenomenon, the central banks had lost the discipline gold used to impose, and Volcker’s money-supply squeeze proved that controlling the quantity of money controlled the price level — at a brutal but real cost. For a regime in which the multiplier was stable and money demand well-behaved, Friedman’s rule worked. But notice the qualifier the thread has earned by now: monetarism was the right theory of that regime. When QE tripled the base and inflation did not follow, the stable multiplier monetarism assumed had dissolved, and the rule that had vanquished 1970s inflation no longer described the world.
Now Modern Monetary Theory, taken at its strongest, because it is the claim this thread is uniquely placed to weigh and the one most often caricatured. The serious MMT claim is a balance-sheet observation, not a political slogan: a government that issues its own floating currency can always create the money to pay any debt denominated in that currency, so its true constraint is not finance — it can never “run out” — but real resources and inflation. The post-2008 decade was its evidence: central banks created money on a vast scale and the feared inflation did not arrive, because the binding constraint was demand and idle capacity, not a money ceiling. As a diagnosis of how a fiat-currency state’s finances actually work, this is more right than the household-budget analogy that dominates public debate, and the QE era demonstrated it.
The case for MMT ends, though, exactly where its policy advice begins, and the distinction matters. Its diagnosis — the issuer faces a real-resource constraint, not a financing one — is sound. Its prescription — spend up to the inflation limit and adjust with taxes when you hit it — overestimates how fast a political system can read and respond to that limit in real time. The 2021–22 inflation is the honest counter-evidence: when demand finally outran capacity, the inflation came hard and the fiscal brakes did not arrive on the timetable the theory assumes. So the calibrated read is that MMT’s account of what money is in a fiat regime is largely right, and its confidence about steering by that account is not yet earned. For the frontier beyond — whether central-bank digital currencies are the next step in the regime — that live debate has its own home.
“The eye has never seen, nor the hand touched a dollar. All that we can touch or see is a promise to pay or satisfy a debt due for an amount called a dollar.”
— A. Mitchell-Innes, “What Is Money?”, Banking Law Journal, 1913
Is money just credit — an IOU all the way down?
Banks create money by lending; states create it by spending. On the credit view, every dollar is somebody’s promise, and the metal was only ever one way to settle the promise. Powerful as a description of the modern regime — and easy to push too far into policy.
Where the thread lands — what money is
So: what is money? Two answers, and they are the same answer at two altitudes. Functionally, money is the thing the whole thread has tracked — the medium of exchange, the unit of account, the store of value. Institutionally, in the regime we actually live in, money is a state-backed credit instrument that evolved out of commodity origins. The metallists were right about the origin and about why commodity money was stable: you cannot print gold. The chartalists are right about what fiat money is and why it holds value without any metal at all: the state denominates obligations in it and takes it back. The synthesis is not a fudge — it is the history. Money began as a commodity, became a state liability, and is now a credit instrument, and each definition was the true one for its regime.
That is why no single theory has ever stayed right. The quantity theory was true under metallic and gold regimes; monetarism captured the early-fiat era and proved itself against 1970s inflation; and the post-2008 QE regime — where tripling the base moved nothing — is exactly the environment where the inherited mechanics broke and the live debates over credit, endogenous money, and fiscal backing revived. The theory of money has always been the theory of its regime; the field is unsettled now not because economists have lost their grip but because the fiat-and-QE regime is genuinely new, and the apparatus they inherited was built for regimes that no longer exist.
Three of these claims sit at different confidence levels, and the thread should say which is which. That money is functionally and institutionally defined is settled consensus across the mainstream. The historical-origin question — did money begin in barter and commodity, or in credit and the ledger? — is a method-and-evidence split: the anthropological record of temple-ledger credit running ahead of coinage is, honestly, stronger than the textbook barter story, while commodity money’s stability properties are also real, so the verdict reports the tension rather than crowning a winner. And the post-2008 questions — does QE work, is MMT serious, are CBDCs wise — are a live frame-and-method split inside an active research area, where the thread lands its calibrated reads (MMT’s diagnosis beats its prescription; QE worked as a financial backstop but not as a reliable inflation lever; the quantity-theory mechanics are regime-broken today) without pretending the field has closed the case.
For the present-day arguments at full debate depth — the three live controversies this thread deliberately does not relitigate — the across-eras view hands off to its companions: What is money, actually? takes the MMT, Bitcoin, and dollar-dominance debates head-on; Does government spending help the economy? works the MMT and fiscal-theory question inside the stimulus debate; and Can central banks control the economy? tells the central-bank side of the modern regime story.
The thread, in four paired rungs
Follow the whole arc and you see one object — money — refusing to hold still, with the theory of it and the practice of it dragging each other forward in lockstep:
- Metal, on coinage. Money was the metal in thought (bullionism) and in the purse (metallic coinage). Theory and regime agreed completely — until debasement showed that what mattered was what the coin bought, not what it was made of.
- Veil, on the gold standard. The quantity theory made the quantity of money, not its substance, the thing that set prices — and the classical gold standard was that theory cast in institutions, a self-regulating specie-flow that made money roughly neutral because the regime forced it to be.
- State liability, on Bretton Woods. The metallic regime broke in the interwar collapse, money kept working without gold, and theory relocated — to the state that demands the token (chartalism) and the expectations that govern whether people spend or hoard it (Keynes). Bretton Woods was the half-metallic compromise that bridged the way to full fiat.
- Credit, in the fiat-and-QE regime. Nixon cut the last gold thread in 1971; monetarism disciplined the early fiat era; and after 2008, when tripling the money base moved nothing, the credit-and-state-liability view revived, because the old quantity mechanics had stopped describing the world.
The signature lesson is not that the later theories beat the earlier ones. It is that each theory was the true theory of its own regime, and was overturned only when the regime moved beneath it. Bullionism was right about a metallic world; the quantity theory was right under gold; chartalism and liquidity preference were right once the metal let go; the credit view is right about the fiat regime we inhabit. The theory of money has always been the theory of its regime — which is the deepest reason the question stays open: every time we think we have answered “what is money,” the regime changes the answer.
That is also why this thread stops at the threshold of the live arguments rather than entering them. The present-day controversies — whether a currency-issuer faces a real financing constraint, whether QE works, whether crypto or a central-bank digital currency is the next regime rung — are debates about a regime that is still being built, and they live where they can be argued at depth: What is money, actually?, Does government spending help the economy?, and Can central banks control the economy? This walkthrough is the long view that puts those arguments in their place in the thread.