What Money Is and What It Does

Before money, trade required a double coincidence of wants: a fisherman who wants shoes has to find a shoemaker who happens to want fish, right now. That almost never happens, so barter economies waste huge amounts of time just searching for trading partners. Money fixes this because it works as a medium of exchange, something everyone accepts in trade. The fisherman sells fish for money to anyone, then uses that money to buy shoes from the shoemaker, who never had to want fish at all.

Money does two other jobs beyond that. As a unit of account, it gives a common price scale so a car and a cup of coffee can be compared in the same units, which is exactly how nominal GDP gets measured: every good and service priced in dollars and added up. As a store of value, money lets purchasing power sit still, so you can earn income today and spend it next month without it rotting or spoiling like a barter good might. That store-of-value job breaks down during hyperinflation: when prices double every few days, holding cash means watching its purchasing power evaporate, so people rush to spend money the instant they get it or switch to a more stable currency instead.

Money is also easy to confuse with wealth or income, but the three are not the same. Wealth is the total value of everything you own, stocks, houses, cars, minus debts, at a point in time. Income is a flow of earnings over a period, like a paycheck every month. Money is just the subset of your assets held as cash or checking balances, ready to spend right now. This distinction matters going forward, because the next topics build the money market on exactly this narrow definition of money, not on wealth or income.