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What Is Money: The Three Essential Functions Explained

Money is everywhere in modern life. You earn it, spend it, save it, and worry about it. But despite its omnipresence, most people can't answer a simple question: what exactly is money?

The answer is surprising: money isn't just one thing. Money is three completely different functions operating simultaneously. If you lose even one of those functions, the entire system breaks. Understanding these three functions is the key to understanding not just what money is, but why inflation matters, why economic crises happen, and how financial systems collapse.

In this article, we'll explore each of money's three essential functions, show how they work together, examine what happens when they fail, and explain why this framework helps economists predict economic problems before they occur.

Quick definition: Money performs three functions simultaneously: it acts as a medium of exchange (what you trade with), a unit of account (how you measure value), and a store of value (what you save). All three must work together.

Key takeaways​

  • Medium of exchange: Money solves the double coincidence problem by letting you trade with anyone, anytime, without needing what they have or them needing what you have
  • Unit of account: Money provides a standard measure of value, eliminating endless negotiation and enabling accounting and planning
  • Store of value: Money allows you to save purchasing power across time, though inflation can seriously damage this function
  • All three functions are required: If even one fails, money stops functioning effectively, even if the other two work perfectly
  • Hyperinflation destroys the store-of-value function: People still use the currency to trade (medium of exchange) and price goods (unit of account), but they stop saving it
  • Different objects can serve as money: The three-function framework explains why cowrie shells, gold, paper notes, and digital currencies all work as money

Function 1: Medium of Exchange — The Translation Layer​

Money's first function is to act as a medium of exchange. This is money's most visible job: it's what you use to buy things.

Think of money as a translator. In a barter economy, you need two specialized transactions: you must sell what you have, and then buy what you want. But both sides must align perfectly. You're a computer repair specialist. Your neighbor grows apples. You need apples. But your neighbor doesn't need computer repair this week.

Under barter, trade fails. Under money, it flows:

  1. You perform computer repair for a customer (who doesn't need apples)
  2. That customer pays you in money
  3. You trade that money to your apple-growing neighbor (who doesn't care about computer repair)
  4. You get apples

Money sits in the middle, separating the two transactions. This separation is everything. It's the difference between a civilization that can support millions of people and one that's stuck in small villages.

Historical Examples of Medium-of-Exchange Failure​

Modern hyperinflation case: Venezuela (2015-2025)

In 2015, the Venezuelan bolívar was worth roughly 215 bolívares per U.S. dollar. By 2020, it was 200,000 bolívares per dollar. By 2025, it was millions. Technically, the bolívar still functioned as a medium of exchange. You could walk into a store and buy milk with bolívares.

But the speed of collapse meant that money sat in your wallet and lost value by the hour. People faced a choice: keep the bolívar and watch it evaporate, or immediately trade it for dollars or goods. Transaction velocity skyrocketed. Stores raised prices daily. The medium-of-exchange function technically remained, but it was so damaged that the entire economy nearly froze.

Historical case: Eastern Europe post-1989

When East German marks became worthless after German reunification, people couldn't use them as a medium of exchange anymore. Theoretically, you could still hand someone an East German mark. Practically, no one accepted them. The government had to swap them for Deutsche Marks. The medium-of-exchange function collapsed, and the currency became worthless overnight.

Why Medium-of-Exchange Matters​

This function solves the double coincidence of wants problem we explored in article one. Without a medium of exchange, economies are stuck in barter. With one, billions of transactions happen daily.

The medium-of-exchange function is so powerful that it's often all people notice. "I use money to buy things," is the most obvious description of money's purpose. But it's only one of three.

Function 2: Unit of Account — The Measuring Stick​

Money's second function is less obvious but equally essential: it acts as a unit of account. This means money provides a standard way to measure and compare the value of different things.

Instead of saying "this shirt costs one chicken or three loaves of bread or one-twentieth of a cow," we say "this shirt costs $15." Everyone knows what $15 is. Prices are standardized and comparable.

How Unit of Account Enables Accounting​

A baker running a business needs to know: did I make money this month? Under barter, this is nearly impossible. How do you compare the value of sheep you traded against apples you traded against leather you traded?

With money as a unit of account:

  • Monday: I sold 50 loaves for $2 each = $100 revenue
  • Tuesday: I sold 60 loaves for $2 each = $120 revenue
  • Wednesday: I sold 40 loaves for $2 each = $80 revenue
  • Weekly total: $300 revenue

Now compare to costs:

  • Flour: $100
  • Labor: $120
  • Rent: $40
  • Profit: $40

The unit-of-account function makes this calculation possible. Without it, a business owner can't tell if they're profitable.

The Concrete Problem Barter Creates​

Imagine a barter economy where prices vary wildly:

  • Monday: one sheep = 10 eggs
  • Tuesday: one sheep = 15 eggs (chickens got sick, eggs are rarer)
  • Wednesday: one sheep = 8 eggs (a new flock arrived)
  • Thursday: one sheep = 12 eggs

A shepherd sold one sheep on Monday for 10 eggs. On Thursday, a sheep is worth 12 eggs. Did the shepherd make a profit or lose money? You can't tell because the value of "one sheep" changes relative to "one egg" constantly.

In real barter economies (documented in ancient Mesopotamian records), this variability was constant and destructive. Merchants couldn't plan. They couldn't calculate profit. They couldn't even tell if they were being cheated because values were so subjective.

Historical evidence from clay tablets shows that ancient societies attempted to stabilize this with "official" exchange rates: "The king declares one sheep equals ten eggs always." But the rates were arbitrary and unrealistic, so people ignored them.

Modern Unit-of-Account Examples​

Your salary: "I earn $50,000 per year" is meaningful because dollars are a unit of account. You can compare this to "$40,000 per year" and see you're earning 25% more. You can compare it to the cost of living: "Rent is $1,200 per month, so on my salary I can afford a place that costs $600 per month in rent."

Try doing this with barter: "I earn 50 chickens per year. My rent is 2 cows. Can I afford it?" You'd have to calculate the exchange rate between chickens and cows, which varies by season and market conditions. Your entire financial future becomes uncertain.

Credit and debt: To borrow money, you need to know what you owe. "I borrowed $10,000, and I'll repay $10,500 in one year" is clear. The amount owed is expressed in a standard unit.

In barter, this breaks. "I borrowed 100 pounds of grain, and I'll repay it with 120 pounds of grain in one year." But what if the grain harvest fails and grain doubles in value? You owe much more than you borrowed. What if grain surpluses make it worth half as much? You're being robbed. Credit becomes impossible to structure fairly.

The Unit-of-Account Function Under Hyperinflation​

Venezuela again provides a clear example. By 2020, the bolívar was moving so fast that:

  • Stores couldn't display prices (they changed hourly)
  • Restaurants printed menus with no prices; prices were quoted verbally and changed by customer
  • Workers got paid but the money lost value before they could spend it
  • Unit of account broke: you couldn't know what anything actually cost

The bolívar still technically worked as a medium of exchange and unit of account (prices were still quoted in bolívares). But the unit was so unstable that people abandoned it mentally. Merchants switched to quoting prices in U.S. dollars. The bolívar stopped functioning as a meaningful unit of account.

Function 3: Store of Value — The Time Machine​

Money's third function is perhaps the most fragile: it acts as a store of value. This means money can hold its worth across time.

You earn $1,000 today. You spend it three months from now. The $1,000 hasn't lost purchasing power (ideally). This is the time-travel function. It lets you move value from the present into the future.

Why Store of Value Matters​

A farmer in a barter economy faces a timing problem. He produces grain once per year at harvest. But he needs food year-round. So he stores grain. This works, but grain spoils. After six months, 20% of the grain is gone to rot and insects. After a year, 50% is gone.

Money solves this. The farmer sells his annual grain harvest for money. He spends that money gradually throughout the year. No spoilage. No deterioration.

More broadly, the store-of-value function enables:

Savings: You can earn money today and use it months or years from now. This lets you buy a house, save for education, or prepare for emergencies.

Investment: A merchant can accumulate money from many trades, then use that accumulated value to fund a larger venture (a trade expedition, a craft workshop, etc.).

Insurance: You save money in good years to survive bad years.

Historical Examples of Store-of-Value Failure​

German hyperinflation (1923):

In early 1923, a loaf of bread cost 250 marks. By summer, it cost 100,000 marks. By November, it cost over 200 billion marks. A person who saved 1,000 marks in January could buy four loaves of bread. By December, those 1,000 marks couldn't buy a single loaf.

The German Mark failed as a store of value. As a medium of exchange, it still "worked"—people still traded with it—but only because they immediately converted it into something more stable (foreign currency, gold, real estate). Money that was kept overnight lost 50% or more of its value.

Modern U.S. inflation (2021-2024):

The U.S. experienced 9% inflation in 2022 alone. Someone who had $10,000 in savings at the start of 2022 could buy goods worth $10,000. By the end of the year, those same goods cost $10,900. The store-of-value function degraded. Not catastrophically (the currency still worked), but noticeably.

The cowrie shell collapse (1800s):

Cowrie shells were excellent money for 800 years. Then Europeans began flooding African markets with cheap shells. Suddenly, shells were abundant. They no longer stored value. A person who saved 1,000 shells in 1790 found their purchasing power cut in half by 1810 as shells became worthless. The store-of-value function collapsed.

The Three Functions Under Economic Stress​

These three examples show a pattern: when store-of-value fails, medium-of-exchange and unit-of-account can still technically work, but the currency becomes unusable.

In Venezuela, stores still quoted prices in bolívares and people still traded with bolívares—the medium-of-exchange and unit-of-account functions persisted. But people wouldn't hold bolívares overnight because store of value had failed. They immediately converted to dollars.

This creates a vicious cycle:

  1. Store of value fails (prices rise faster than wages)
  2. People stop saving money
  3. People stop trusting the currency
  4. Medium of exchange fails (fewer people accept it)
  5. The currency dies

How All Three Functions Work Together​

A good currency needs all three functions working simultaneously. If you remove any one, the system cracks.

If Medium of Exchange Fails​

Imagine a currency that's an excellent unit of account and store of value, but nobody accepts it for trade.

This actually describes gold bullion today. Gold is:

  • A great store of value (gold prices have been relatively stable over centuries)
  • An acceptable unit of account in some contexts (precious metals are priced in grams of gold)
  • But a terrible medium of exchange (you can't walk into a grocery store and pay with gold bars)

Gold used to be money. It stopped being money the moment people stopped accepting it for everyday transactions. Now it's a commodity and a store of value, but not money.

If Unit of Account Fails​

Imagine a currency where prices are meaningful one day and meaningless the next.

Early Bitcoin somewhat struggled with this. Bitcoin's value was so volatile that merchants couldn't price things in Bitcoin. A coffee seller would quote a Bitcoin price, but Bitcoin would drop 30% by the next day. Was the merchant losing money? Making money? Impossible to tell.

The medium-of-exchange function worked (people could trade in Bitcoin). The store-of-value function somewhat worked (Bitcoin recovered from crashes). But unit of account failed—you couldn't meaningfully price goods in Bitcoin.

As Bitcoin matured and stabilized, this improved. But during early adoption and volatility surges, unit of account was damaged.

If Store of Value Fails​

This is what happened in Venezuela, Germany 1923, and during the cowrie shell collapse.

Medium of exchange still works—people can trade with the currency. Unit of account still works—prices are quoted in the currency. But nobody saves. Nobody plans for the future. The currency becomes a hot potato: you grab it, immediately spend it, and pass it to the next person.

This is actually why hyperinflation is so economically destructive. It's not that trade becomes impossible—people still exchange goods. It's that planning becomes impossible. No one invests in building a business. No one saves for education. Everyone focuses on immediate survival.

Why Economists Use This Framework​

The three-function framework is powerful because it predicts which problems will destroy a currency:

If inflation rises to 5% annually:

  • Medium of exchange: fine
  • Unit of account: fine (prices adjust)
  • Store of value: damaged (your savings lose 5% per year)

This economy still functions, but savers are hurt. People shift to investment and gold.

If inflation hits 50% monthly (Venezuela's 2016 level):

  • Medium of exchange: failing (fewer businesses accept the currency)
  • Unit of account: failing (prices change so fast pricing is impossible)
  • Store of value: destroyed (savings evaporate)

This economy nearly freezes.

If medium of exchange fails but exchange rates are stable: This describes situations like the 1931 Great Depression's deflationary spiral, where people stopped trusting banks and hoarded cash. People still technically could trade with currency, but they wouldn't, because they'd lost confidence. Economic activity collapsed even though the currency theoretically remained "sound."

Real-World Examples: Money Losing Functions​

Example 1: U.S. Dollar During 1970s Stagflation​

During the 1970s, U.S. inflation averaged 7% annually (reaching 13.5% in 1980). The three functions:

  • Medium of exchange: worked fine (people still traded)
  • Unit of account: worked but was confusing (people had to constantly update their mental model of prices)
  • Store of value: damaged (savings were eroded significantly)

Result: People moved savings into real estate and precious metals. Nominal stock market was flat for a decade even though corporate earnings grew. Savers were hurt, but the currency didn't collapse because the other two functions remained strong.

Example 2: Argentine Peso (2001-2002 Crisis)​

Argentina's currency collapsed when:

  • Medium of exchange: people stopped accepting pesos
  • Unit of account: the government tried to legally override market reality (forcing 1:1 peso-to-dollar exchanges despite inflation)
  • Store of value: destroyed (savings were frozen in banks)

Result: Economic collapse, riots, and the peso's value crashed 75% before stabilizing.

Example 3: Zimbabwe Dollar (2008-2009)​

Zimbabwe's currency experienced hyperinflation exceeding 89.7 sextillion percent annually (that's 10^21 percent). All three functions failed completely. The currency became worthless. The country abandoned the Zimbabwe dollar and adopted the U.S. dollar, South African rand, and other foreign currencies.

Common Mistakes About Money's Functions​

Mistake 1: "Money's Main Function is Store of Value"​

Many people think money's primary purpose is to save. Actually, medium of exchange is the primary function. Store of value is important but secondary. This mistake leads people to believe that inflation is money's greatest problem. Actually, moderate inflation (2-3% annually) is acceptable if the other two functions work. But high inflation that destroys the store-of-value function creates real damage.

Mistake 2: "If the Government Says It's Money, It's Money"​

Government authority doesn't create money; consensus does. The government can declare something is legal tender, but if people won't accept it, it won't function as money. People accept government-issued money because:

  1. Everyone else accepts it (consensus)
  2. The government keeps it relatively stable (so it stores value)
  3. Laws enforce its legal status in contracts

But the law is the least important factor. Cowrie shells became money without legal backing. Zimbabwe's currency became worthless despite legal backing. Government declaration is necessary but not sufficient.

Mistake 3: "Money Needs to Be Backed by Gold to Be Real"​

The three-function framework shows that "backing" is irrelevant. Money is backed by consensus and utility. If an object functions as medium of exchange, unit of account, and store of value, it's money—regardless of whether it's backed by anything.

Cowrie shells weren't backed by gold. Modern fiat dollars aren't backed by gold. Bitcoin isn't backed by anything physical. They work because they perform all three functions.

Mistake 4: "Digital Money Isn't Real Money"​

Digital money (bank accounts, PayPal, Venmo) performs all three functions perfectly:

  • Medium of exchange: you can spend it
  • Unit of account: prices are quoted in dollars
  • Store of value: your balance stays the same (assuming no inflation)

The fact that it's digital is irrelevant to whether it's money. Money is defined by function, not form.

Frequently Asked Questions​

What makes something "good" money vs. "bad" money?​

Good money has stable value (store of value function), is widely accepted (medium of exchange function), and provides clear pricing (unit of account function). Bad money fails at one or more of these. Good money also tends to be durable, portable, and scarce. A good store of value can't be easily copied or created in abundance.

Can something be money if it only performs one of the three functions?​

Technically, yes, for a limited time. Bitcoin was primarily a store of value for years before it became accepted as a medium of exchange. But an object that performs only one function isn't very useful as money. A currency that only stores value but can't be traded isn't money—it's a commodity.

Why does the government care about controlling the money supply?​

The government cares because controlling the money supply affects all three functions:

  • Too little money: medium of exchange doesn't work (not enough to facilitate transactions)
  • Too much money: unit of account breaks (prices become unstable) and store of value fails (inflation erodes savings)
  • Right amount: all three functions work smoothly

Central banks try to manage the money supply to keep inflation moderate (2-3%) so store of value works while not restricting transactions.

What happens if store of value fails but medium of exchange still works?​

You get hyperinflation. People still trade (medium of exchange works), but they immediately convert currency to goods or foreign currency. Economic activity may continue, but long-term planning becomes impossible. Businesses don't invest in future capacity. People don't save. Society focuses on immediate survival.

Can a country use a foreign currency as its money?​

Yes, and several do. El Salvador legally adopted the U.S. dollar in 2001. People use the dollar as medium of exchange, unit of account, and store of value. From a functional perspective, the dollar is their money. The dollar performs all three functions, regardless of which country issues it.

Is cryptocurrency real money?​

By the three-function definition, yes—if it performs all three functions. Bitcoin and other cryptocurrencies work as:

  • Medium of exchange: you can buy things with them (though adoption is still growing)
  • Unit of account: prices can be quoted in cryptocurrency
  • Store of value: the value fluctuates, but you can save it

Whether cryptocurrencies are "good" money is debatable. They're volatile (poor store of value), not universally accepted (limited medium of exchange), and not stable enough for reliable unit of account. But they're functional money among people who accept them.

Why do economists care more about inflation than other problems?​

Because inflation directly threatens the store-of-value function. Without a functional store of value, people can't save, plan, or invest. This damages long-term economic growth. Medium of exchange and unit of account tend to be more robust—they work even under stress. But store of value is fragile. Protecting it is central to economic stability.

Summary​

Money performs three essential functions simultaneously: it acts as a medium of exchange (what you trade with), a unit of account (how you measure value), and a store of value (what you save). All three functions are required. If even one fails, money stops working effectively.

The medium-of-exchange function solves the double coincidence of wants problem and enables large-scale economies. The unit-of-account function allows pricing, accounting, and business planning. The store-of-value function enables savings, investment, and long-term planning.

Understanding these three functions explains why inflation is economically destructive, why hyperinflation causes economic collapse despite people still technically trading in the currency, and why money itself is defined by function rather than form or government backing. Cowrie shells, fiat currency, and digital money all work as money when they perform all three functions successfully.

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