We use money every day without ever asking what it actually is. That is fine for spending — but it makes it impossible to judge whether something new, like Bitcoin, counts as money. So before comparing anything, we need a clear, neutral definition. The good news: money is not mysterious. It is a tool, and like any tool, it is defined by the jobs it does.

The three jobs of money

Across every culture and century, money has been asked to do three things.

A medium of exchange. Money is the thing you trade through rather than the thing you ultimately want. Instead of swapping your work directly for bread, you accept money for your work and hand money to the baker. It sits in the middle of every transaction, which is why it has to be something other people will reliably accept.

A store of value. Money lets you move value across time. You earn today and spend next month, or next year, trusting that what you set aside keeps roughly the same buying power. A money that leaks value quickly fails at this job, even if it works fine for a quick purchase.

A unit of account. Money is the ruler we measure worth with. Prices, wages, debts, and profits are all quoted in the same units, which lets us compare a loaf of bread to an hour of work to a house. Without a common unit, every price would be a separate barter negotiation.

A useful way to remember the order: something usually becomes a medium of exchange first, proves itself as a store of value over time, and only then settles into being the unit everyone quotes prices in.

Why barter is not enough

To see why money matters, picture a world without it. You grow apples and want shoes. You have to find a shoemaker who happens to want apples, right now, in the amount you can offer. Economists call this the coincidence of wantsThe unlikely situation where two people each have exactly what the other wants, in the right amounts, at the same time — the core problem barter creates. — and it almost never lines up. Money dissolves the problem. The shoemaker does not need to want apples; they only need to want money, because money buys whatever they do want.

What makes something good at the job

Here is the key move, the one this entire site is built on. Many things have served as money — cattle, salt, shells, beads, silver, gold, paper notes. They were not chosen at random. The ones that lasted shared a set of physical and practical traits. We can turn those traits into a checklist, and then hold any candidate up against it. These are the properties of good money:

• Scarcity — the supply is limited and hard to expand, so it holds value.
• Durability — it survives over time without rotting or breaking.
• Portability — you can move value easily, ideally across distance.
• Divisibility — it splits into small units for small purchases.
• Fungibility — one unit is interchangeable with any other.
• Verifiability — you can confirm it is genuine.
• Censorship-resistance — a third party cannot easily block or seize it.
• Predictable policy — the rules governing its supply are known and stable.

Notice how the properties map onto the jobs. Portability, divisibility, and verifiability make something a good medium of exchange — they make trade smooth. Scarcity, durability, and predictable policy make something a good store of value — they protect your buying power over time. Fungibility underpins the unit of account, because a ruler only works if every unit is identical.

Good money is not a matter of opinion. It is whatever scores well on a checklist any of us can apply.

This is what makes the framework so powerful. You do not have to take anyone's word about gold, the dollar, or Bitcoin. You can ask, property by property, how well each one actually holds up — and reach your own conclusion.

Money is a technology

One last reframing. It helps to think of money not as a fixed thing handed down by authorities, but as a technology for storing and moving value — one that has been quietly upgraded for thousands of years. Shells gave way to metal; metal coins gave way to paper claims on metal; paper claims gave way to pure government-issued currency. Each step changed how well money scored on the properties. Seen this way, the real question is not "is Bitcoin money?" but "on the properties that matter, is it an upgrade, a downgrade, or a sideways move?" The rest of this series is built to help you answer that.