U4.3 Definition, Measurement, and Functions of Money
Master AP Macro 4.3: the three functions of money, M1 vs M2 measures of the money supply, and why high inflation destroys money's store of value.
What you'll do in this lesson
A voice-first session with the Crimsora tutor on U4.3 Definition, Measurement, and Functions of Money, then targeted practice and FRQs — with the tutor adapting to where you get stuck.
What this lesson covers
Money seems obvious until an exam question asks you to explain exactly what makes something "money" or which measure of the money supply includes savings deposits. In AP Macroeconomics Topic 4.3, you learn that money is defined not by what it looks like but by what it does. This lesson breaks down the three functions of money, distinguishes the M1 and M2 money supply measures, and shows why high inflation quietly erodes one of money's core jobs. Nail this foundation now, because Units 4 and 5 build directly on it when you analyze the money market and monetary policy.
The Three Functions of Money
Economists define money by its functions, not its physical form. Anything that reliably performs these three jobs qualifies as money.
First, money is a medium of exchange: it is generally accepted as payment for goods and services. This solves the problem of barter, which requires a "double coincidence of wants" (both parties must want what the other offers). With money, a teacher does not need to find a farmer who wants economics lessons.
Second, money is a store of value: it lets you hold purchasing power over time. You can earn money today and spend it next month because it retains value. This function is imperfect and depends on stable prices.
Third, money is a unit of account: it provides a common measuring stick for prices. Listing a laptop at 800 dollars and a shirt at 20 dollars lets you compare value instantly, the way meters measure distance.
A common exam trap: describing money "holding its value over time" is the store of value, while "pricing everything in dollars" is the unit of account. Read the verbs carefully.
First, money is a medium of exchange: it is generally accepted as payment for goods and services. This solves the problem of barter, which requires a "double coincidence of wants" (both parties must want what the other offers). With money, a teacher does not need to find a farmer who wants economics lessons.
Second, money is a store of value: it lets you hold purchasing power over time. You can earn money today and spend it next month because it retains value. This function is imperfect and depends on stable prices.
Third, money is a unit of account: it provides a common measuring stick for prices. Listing a laptop at 800 dollars and a shirt at 20 dollars lets you compare value instantly, the way meters measure distance.
| Function | What it does | Everyday example |
|---|---|---|
| Medium of exchange | Accepted for transactions | Paying for lunch with cash |
| Store of value | Holds purchasing power over time | Saving for next semester |
| Unit of account | Common measure of prices | Comparing sticker prices |
Commodity vs. Fiat Money and Liquidity
Money comes in two broad types. Commodity money has intrinsic value apart from its use as money, like gold or silver coins. Fiat money has no intrinsic value and is money only because a government declares it legal tender and people accept it. Modern U.S. dollars are fiat money.
A key concept underlying money measurement is liquidity, the ease and speed with which an asset can be converted into cash without losing value. Cash is perfectly liquid. A checking deposit is highly liquid. A savings account is somewhat less liquid, and assets like real estate or stocks are far less liquid.
Liquidity is why economists rank assets on a spectrum and group them into official money supply measures. The more liquid an asset, the more it functions directly as a medium of exchange. This ordering matters because M1 and M2 are essentially organized by liquidity: the narrowest measure holds the most liquid assets, and broader measures add progressively less liquid "near-monies."
A misconception to avoid: credit cards are NOT money. A credit card is a short-term loan that defers payment; the money involved is what sits in your bank account when you pay the bill. Similarly, stocks and bonds are financial assets, not money, because they are not directly used as a medium of exchange and can lose value when converted to cash.
A key concept underlying money measurement is liquidity, the ease and speed with which an asset can be converted into cash without losing value. Cash is perfectly liquid. A checking deposit is highly liquid. A savings account is somewhat less liquid, and assets like real estate or stocks are far less liquid.
Liquidity is why economists rank assets on a spectrum and group them into official money supply measures. The more liquid an asset, the more it functions directly as a medium of exchange. This ordering matters because M1 and M2 are essentially organized by liquidity: the narrowest measure holds the most liquid assets, and broader measures add progressively less liquid "near-monies."
A misconception to avoid: credit cards are NOT money. A credit card is a short-term loan that defers payment; the money involved is what sits in your bank account when you pay the bill. Similarly, stocks and bonds are financial assets, not money, because they are not directly used as a medium of exchange and can lose value when converted to cash.
Measuring the Money Supply: M1 vs. M2
Because "money" ranges from cash to near-cash, economists use tiered measures. On the AP exam you need M1 and M2.
M1 is the narrow measure containing the most liquid assets: currency in circulation (cash held by the public, not in bank vaults), checkable/demand deposits, and other highly liquid deposits.
M2 is broader. It includes everything in M1 PLUS somewhat less liquid "near-monies" such as savings deposits, small-denomination time deposits (small CDs), and retail money market accounts. Because M2 contains M1, M2 is always larger than M1.
Exam tips and traps: currency held inside bank vaults is NOT counted (only currency in circulation counts). Large-denomination items, stocks, bonds, and credit are excluded from both. When a question asks you to classify an item, first decide its liquidity, then place it. A savings account belongs in M2 only; a checking deposit belongs in both M1 and M2 because M2 contains all of M1. Questions often give a table of items and ask you to sum up M1 or M2 — practice adding only the qualifying categories.
M1 is the narrow measure containing the most liquid assets: currency in circulation (cash held by the public, not in bank vaults), checkable/demand deposits, and other highly liquid deposits.
M2 is broader. It includes everything in M1 PLUS somewhat less liquid "near-monies" such as savings deposits, small-denomination time deposits (small CDs), and retail money market accounts. Because M2 contains M1, M2 is always larger than M1.
| Measure | Includes | Liquidity |
|---|---|---|
| M1 | Currency in circulation, checkable/demand deposits | Highest |
| M2 | All of M1 plus savings deposits, small time deposits, money market accounts | High but lower than M1 |
Why High Inflation Undermines Store of Value
Money's store-of-value function assumes prices stay reasonably stable. Inflation is a sustained rise in the general price level, which means each dollar buys fewer goods over time. When inflation is high, money loses purchasing power quickly.
Suppose you hold 1,000 dollars in cash and annual inflation is 3 percent. A year later that cash buys roughly 3 percent less — still a modest erosion. But if inflation is 50 percent per year, your 1,000 dollars buys about a third less purchasing power within months, and the loss compounds. People respond by spending money as fast as they receive it, converting it into goods or more stable assets. In hyperinflations, money can become nearly worthless as a store of value.
Crucially, high inflation attacks the store-of-value function most directly, while the medium-of-exchange and unit-of-account functions can also degrade if inflation gets extreme (people may switch to a foreign currency or barter). But for AP purposes, the clean answer is: high inflation reduces money's purchasing power over time, weakening its ability to store value.
Connect this to Topic 4.2: real values adjust nominal values for inflation. The real value of money falls as prices rise. This is also why lenders and savers dislike unexpected inflation — the money repaid or withdrawn later buys less than the money originally lent or deposited.
Suppose you hold 1,000 dollars in cash and annual inflation is 3 percent. A year later that cash buys roughly 3 percent less — still a modest erosion. But if inflation is 50 percent per year, your 1,000 dollars buys about a third less purchasing power within months, and the loss compounds. People respond by spending money as fast as they receive it, converting it into goods or more stable assets. In hyperinflations, money can become nearly worthless as a store of value.
Crucially, high inflation attacks the store-of-value function most directly, while the medium-of-exchange and unit-of-account functions can also degrade if inflation gets extreme (people may switch to a foreign currency or barter). But for AP purposes, the clean answer is: high inflation reduces money's purchasing power over time, weakening its ability to store value.
Connect this to Topic 4.2: real values adjust nominal values for inflation. The real value of money falls as prices rise. This is also why lenders and savers dislike unexpected inflation — the money repaid or withdrawn later buys less than the money originally lent or deposited.
Key terms
- Medium of exchange.
- The function of money by which it is generally accepted as payment for goods and services, eliminating the need for barter.
- Store of value.
- The function of money that allows it to hold purchasing power over time, so it can be saved and spent later.
- Unit of account.
- The function of money that provides a common measure for stating and comparing the prices of goods and services.
- Fiat money.
- Money with no intrinsic value that serves as money because a government declares it legal tender and people accept it.
- Liquidity.
- The ease and speed with which an asset can be converted into cash without significant loss of value.
- M1.
- The narrow money supply measure including currency in circulation, checkable/demand deposits, and other highly liquid deposits.
- M2.
- The broader money supply measure including all of M1 plus savings deposits, small time deposits, and money market accounts.
- Currency in circulation.
- Cash held by the public outside of banks; cash sitting in bank vaults is excluded from money supply measures.
Worked example
A student is given the following amounts (in billions): currency in circulation = 400, checkable deposits = 600, savings deposits = 1,200, small-denomination time deposits = 300, and corporate stocks = 500. Calculate M1 and M2.
Start with M1, the most liquid assets: currency in circulation plus checkable deposits. That is billion, so M1 equals 1,000 billion.
Now build M2, which includes all of M1 plus the less liquid near-monies: savings deposits and small-denomination time deposits. So M2 equals billion.
Notice what we excluded. Corporate stocks (500) are a financial asset, not money — they are not a medium of exchange and can lose value when sold, so they appear in neither M1 nor M2. Also confirm we used currency in circulation (public cash), not vault cash, which would be excluded.
The answer: M1 = 1,000 billion and M2 = 2,500 billion. Because M2 always contains M1, M2 must be larger, which our numbers confirm.
Now build M2, which includes all of M1 plus the less liquid near-monies: savings deposits and small-denomination time deposits. So M2 equals billion.
Notice what we excluded. Corporate stocks (500) are a financial asset, not money — they are not a medium of exchange and can lose value when sold, so they appear in neither M1 nor M2. Also confirm we used currency in circulation (public cash), not vault cash, which would be excluded.
The answer: M1 = 1,000 billion and M2 = 2,500 billion. Because M2 always contains M1, M2 must be larger, which our numbers confirm.
Practice questions
Which of the following would be included in M2 but NOT in M1?
- Currency held by the public
- A checkable demand deposit
- A savings deposit
- A share of corporate stock
Answer: A savings deposit
M1 contains only the most liquid assets: currency in circulation and checkable deposits. Savings deposits are less liquid near-monies, so they are added in M2 but excluded from M1. Currency and checkable deposits appear in both measures, and corporate stock is a financial asset excluded from both.
Explain why a period of very high inflation weakens money's function as a store of value but has less immediate effect on its function as a unit of account. Use the concept of purchasing power.
Answer: High inflation rapidly reduces the purchasing power of each dollar, so money held over time buys fewer goods — directly undermining store of value. Prices can still be quoted in the currency, so it can continue functioning as a unit of account, at least until inflation becomes extreme.
The store-of-value function depends on money keeping its value across time; when prices rise sharply, saved money loses purchasing power, so people rush to spend it. The unit-of-account function only requires that prices be expressed in a common measure, which still works even as those numbers climb. A full-credit answer ties the loss of purchasing power explicitly to the store-of-value function.
A country replaces gold coins with paper notes that have no intrinsic value but are accepted because the government declares them legal tender. What type of money is this, and does it still perform the three functions of money?
Answer: This is fiat money, and it can still perform all three functions as long as people accept it and prices remain reasonably stable.
Fiat money has no intrinsic value; its value comes from government designation and public acceptance. It serves as a medium of exchange (accepted in transactions), a unit of account (prices quoted in it), and a store of value (as long as inflation stays low). This shows money is defined by function, not by intrinsic worth.
FAQ
- Is M2 bigger than M1 or the other way around?
- M2 is always larger because M2 includes everything in M1 plus additional near-monies like savings deposits and small time deposits. M1 is the narrower, most-liquid subset contained within M2.
- Are credit cards considered money?
- No. A credit card is a way to borrow short-term, not money itself. The actual money is the balance in your bank account that you use to pay off the card. Neither credit cards nor credit limits are counted in M1 or M2.
- Which function of money does inflation hurt the most?
- Inflation most directly undermines the store-of-value function, because rising prices reduce the purchasing power of money held over time. Extreme inflation can eventually damage the medium-of-exchange and unit-of-account functions too, but store of value is the primary answer on the AP exam.
- Is cash in a bank's vault counted in the money supply?
- No. Only currency in circulation — cash held by the public outside of banks — is counted. Vault cash and bank reserves are excluded from M1 and M2 to avoid double-counting.
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