Why Money Has More Than One Function
A payment, a price tag, and a balance set aside for later may all involve money, but they use it in different ways. Money helps people make exchanges without arranging a direct trade, gives prices a shared way to be stated, and allows purchasing power to be carried from one time to another. These are three distinct economic functions, not three names for the same activity.
Keeping the functions separate is useful when analyzing an unfamiliar situation. A quoted price may use money as a unit of account even if the buyer pays by exchanging something else. A form of money may be widely accepted for current purchases but lose purchasing power over time. The question is not simply whether money appears in the scenario; it is what role it plays.
The Three Functions
As a medium of exchange, money is what a buyer gives a seller to complete an exchange. Without an accepted medium, two people seeking to trade directly must each want what the other offers at the same time. A shared means of payment avoids that matching problem: a baker can sell bread for money and later use the money to buy something else. The baker need not find a seller who wants bread specifically.
As a unit of account, money supplies a common scale for expressing values. If a meal costs 12 units of money and a book costs 18, the buyer can compare their stated prices directly. Without a common unit, each price might instead be expressed as a different quantity of some other good, making comparison more cumbersome. Stating a price in money does not, by itself, mean that money is used to pay.
As a store of value, money lets a person retain the ability to make purchases for a later date. For this function to be useful, money must preserve purchasing power reasonably well over the period in question. If the prices of goods rise while the money balance stays fixed, that balance buys less. Money can therefore serve as a store of value without preserving exactly the same purchasing power.
Functions Are Not the Same as Useful Properties
The functions describe what money does in economic activity. Properties such as acceptability, portability, divisibility, durability, and ease of recognition help explain how well it can do those things. For example, something that is easy to carry and divide into small amounts is more convenient for many transactions. Those characteristics support the medium-of-exchange function; they are not themselves additional functions.
The distinction matters because a useful property does not establish which role something is playing in a particular situation. A durable object might be held for later use, but that fact alone does not show that it is functioning as money. Conversely, a money balance can be used as a unit of account in a price list even though no payment is being made at that moment.
| Role or property | Question to ask | Illustration |
|---|---|---|
| Medium of exchange | Is it accepted to complete a purchase? | A customer pays a vendor for lunch. |
| Unit of account | Are prices or values stated in it? | A menu lists a sandwich at 9 units. |
| Store of value | Is purchasing power being carried to a later time? | A person keeps a balance for a planned purchase. |
| Portability | Is it easy to carry or transfer? | A convenient feature that can help with payments. |
| Durability | Does it resist damage or loss of usability? | A useful feature for retaining value and making repeated exchanges. |
Worked Example: Separating Payment, Price, and Later Use
A hypothetical repair shop lists a tune-up at 80 units of money. A customer pays 50 units immediately and agrees to provide a used bicycle part, valued by both parties at 30 units, to settle the remainder. The shop keeps the 50 units for a planned supply purchase next month. Identify the function or functions shown, and distinguish the money price from the payment method.
Step 1: Identify the unit of account. The tune-up is priced at 80 units, so money is being used as a common measure of the service’s value. The remaining obligation is also expressed in money: \(80-50=30\) units.
Step 2: Identify the medium of exchange. The customer transfers 50 units to the shop as payment. That part of the transaction uses money as a medium of exchange. The bicycle part is also transferred toward settling the bill, but it is not a money payment in this scenario.
Step 3: Identify the store-of-value function. The shop plans to retain the 50 units for a purchase next month. That is an attempt to carry purchasing power forward, so money is serving as a store of value.
Check the accounting. The payments toward the 80-unit price are 50 units in money plus a part valued at 30 units: \(50+30=80\). The mistake to avoid is calling the entire 80-unit price a money payment. The price is stated in money, but only 50 units are paid in money in this scenario.
A Short Justification: Why a Common Unit Helps
A common unit of account makes direct price comparisons possible using the same scale. Suppose two sellers offer the same item for 7 units and 9 units. The difference is immediately \(9-7=2\) units. If the prices were instead stated in different goods, a buyer would first need exchange ratios to translate them into comparable terms. The common unit removes that extra conversion from the comparison.
This justification concerns comparison, not payment. A buyer can compare money prices even if the eventual settlement is made in another agreed form. The unit-of-account function is about how values are expressed; the medium-of-exchange function is about what is used to complete the exchange.
Worked Example: Comparing Offers With a Shared Price Unit
A hypothetical office orders 24 identical desk lamps. Supplier A quotes 15 units per lamp, with a delivery charge of 36 units. Supplier B quotes 16 units per lamp with no delivery charge. Both suppliers state all charges in the same money unit. Which offer has the lower total stated price, and by how much?
Method: Calculate each complete order price in the common unit, including delivery, then compare. This uses money as a unit of account; it does not require assuming how the office will pay.
Supplier A. The lamp charge is \(24\times15=360\) units. Adding delivery gives \(360+36=396\) units.
Supplier B. The lamp charge is \(24\times16=384\) units. Delivery is zero, so the total is \(384+0=384\) units.
Comparison. Supplier B’s stated total is lower by \(396-384=12\) units. The office should not compare only the per-lamp prices: Supplier A’s lower unit price does not account for its delivery charge.
Check. The complete totals are 396 and 384, and their difference is 12. The common mistake is to treat the unit price alone as the total cost or to describe the comparison as a medium-of-exchange example. Here, the relevant function is unit of account.
Money as a Store of Value: Purchasing Power Over Time
A fixed nominal balance does not necessarily represent a fixed quantity of goods. To analyze the store-of-value function, compare the balance with the prices of the goods it could buy. If the relevant price index rises by a factor of 1.10, for example, a balance that stays unchanged has only \(1/1.10\) of its original purchasing power in those goods.
For a simple calculation, suppose a basket costs \(C_0\) at the starting date and \(C_1\) at a later date. A balance \(M\) buys \(M/C_0\) baskets initially and \(M/C_1\) baskets later. The comparison is valid when the basket is held fixed and the stated prices and balance refer to the corresponding dates.
This calculation shows why the store-of-value function is a matter of degree and time period. A balance that retains its nominal amount can still lose purchasing power if prices rise. If its nominal amount also changes, both the balance and the price change must be included in the comparison.
Worked Example: Measuring How Much Purchasing Power Remains
A hypothetical household sets aside 800 units when a chosen basket of goods costs 100 units. One year later, the basket costs 105 units. The balance remains 800 units. How many baskets could the balance buy at each date, and what fraction of its original basket purchasing power remains?
Method and assumptions. Treat the stated basket as unchanged between dates and compare the balance with its price at each date. No interest or other change to the balance is assumed; the only change is the basket price.
At the starting date. The balance buys \(800/100=8\) baskets.
One year later. The balance buys \(800/105=7.619047\ldots\) baskets. To compare with the initial purchasing power, divide the later number by the initial number: \(7.619047\ldots/8=0.952380\ldots\).
Final result. The balance retains about 95.2% of its original basket purchasing power, so about 4.8% has been lost. Round the basket count to three decimals and the percentages to one decimal place. Check: \(7.619/8\) is approximately 0.952, consistent with the result.
Common mistake and correction. It is incorrect to conclude that purchasing power is unchanged because the balance is still 800 units. The basket price increased from 100 to 105, so the correct comparison is \(800/100\) versus \(800/105\), not 800 versus 800 alone.
Common Exam Traps
- Confusing the price with the payment. A price stated in money shows the unit-of-account function. Money serves as a medium of exchange only if it is actually used to make the payment.
- Treating the functions as mutually exclusive. In an ordinary purchase, money can be both the medium of exchange and the unit of account. A balance retained for later can also serve as a store of value.
- Assuming a store of value must hold purchasing power perfectly. The function means that purchasing power can be carried forward, not that it can never change.
- Calling a useful property a function. Portability or durability can make money more convenient, but neither is one of the three functions.
- Comparing nominal balances without considering prices. When the question concerns purchasing power, compare the balance with the prices of goods or a consistent basket.
In practice, the three functions are connected but analytically distinct. The medium of exchange helps people transact; the unit of account helps them state and compare values; and the store of value connects present purchasing power with future choices. Money may perform these roles to different degrees, depending on the circumstances.
Check Your Understanding
For each situation, identify the relevant function or functions and show any requested calculation.
- A hypothetical café lists a meal at 14 units. A customer pays 10 units and agrees to settle the remaining 4 units tomorrow. Which function is shown by the listed price, and how much is paid immediately in money? (Answer: Unit of account; 10 units are paid immediately.)
- A vendor accepts 6 units for a notebook. The buyer later uses the same balance to purchase a snack. Which function is illustrated by the notebook payment? (Answer: Medium of exchange.)
- A household keeps 600 units for later. A fixed basket costs 120 units now and 150 units later, while the balance stays unchanged. How many baskets can it buy at each date? (Answer: 5 baskets now and 4 baskets later.)
- Two hypothetical delivery services quote a 32-unit base charge plus 4 units per package, or a 45-unit base charge plus 3 units per package. For 5 packages, calculate both totals and identify which quote is lower. (Answer: First quote: \(32+5(4)=52\) units; second quote: \(45+5(3)=60\) units; the first is lower by 8 units. The common price unit supports comparison.)
- A balance of 500 units is unchanged while a fixed basket price rises from 80 units to 100 units. Calculate the initial and later basket counts, then state what percentage of initial purchasing power remains. (Answer: \(500/80=6.25\) baskets initially; \(500/100=5\) later; \(5/6.25=0.80\), so 80% remains.)