Money is Trust
How Humanity Lowered the Cost of Cooperation
Last year, I started a series of posts on trust, with Money: More Than Just Stuff, It’s Trust as the focal point. I felt 1-year was a good time to update this account, and extend it.
“Money is the most universal and most efficient system of mutual trust ever devised.” — Yuval Noah Harari, Sapiens: A Brief History of Humankind
If you ask an economist what money is, they will likely give you a functional, three-part definition: it is a unit of account, a store of value, and a medium of exchange. If you ask a dictionary, it will tell you that money is “something generally accepted as a medium of exchange, a measure of value, or a means of payment”.
These definitions are perfectly workable for daily life, but they contain a loophole. Defining money as “something generally accepted” describes a symptom, not a cause. It relies on the word “something,” anchoring our minds to physical objects—gold, silver, paper, or digital ledgers. But the link between an object and its status as money would be severed by a loss of acceptance.
The basic definition is useful, but it’s clear economists do not consider it sufficient. Just this week Stephen Dubner of Freakonomics, released Part 1 of a two-part series, What is Money?, covering an adaptation to an oratorio of Adam Smith’s The Wealth of Nations. Money must be something of a higher order than temporary objects we attach it to.
To understand what money is, we must look past coins and paper. Trust is not merely a social feeling; it is a vital component of cooperation that requires immense social energy to build and maintain. While trust can theoretically be extended freely, reliably creating it at scale carries a real, limiting cost. Money is humanity’s greatest collaborative technology—an accidental invention that survived and spread precisely because it lowered the cost of trust.
The High Cost of Trust
To understand why money is a technology of trust, we have to look at the world before it existed. How do human beings coordinate the exchange of goods and labor without it? Historically, humanity relied on two deeply flawed workarounds: Barter and Kinship.
The Barter Evasion
It’s common to think of barter as a primitive ancestor of money, but it is better to think of it as an attempt to trade without trust.
Imagine you have a surplus of hay, and you need milk. You find a farmer with milk, but he doesn’t need hay; he needs firewood. To make a successful trade, you are forced into a complex puzzle. You must find the person who has firewood and needs hay, trade for the wood, and then return to the dairy farmer. Economists call this the “double coincidence of wants.”
Because there is no trust carrying value across time—no mechanism that says “I gave you milk today, I owe you value tomorrow”—every transaction must be settled immediately, item-for-item. In a physical sense, barter avoids the need for trust, but the friction of searching for perfect matches makes it impossible to scale.
There is also the problem that the neat and tidy view of trust in barter being solved by the direct physical transfer of goods, is a bit of a myth. Anthropological studies of societies without money show trust issues relating to trust on fairness of exchange, both during and after negotiation.
The Kinship Tax
Because barter is so inefficient, early societies rarely relied on it for daily survival. Instead, they relied on kinship networks. Barter was used mostly outside kinship networks.
Early societies solved the trust deficit through deep, interpersonal relationships. You do not barter with your brother, your cousin, or your tribemate. You give them your surplus milk today, trusting implicitly that they will provide you with firewood next winter.
This creates a high-trust environment, but it comes with a fatal flaw: it is unscalable and exclusive. Maintaining deep, bilateral trust requires immense social energy. You can only maintain it with a small, localized group of people—a single-layer network naturally capping around Dunbar’s number of roughly 150 individuals. While societies can attempt to force kinship to scale by creating additional layers of hierarchy, each new layer adds complexity, instability, inefficiency, and immense human costs. This dynamic imposes what writer David Oks has called a “Kinship Tax.” It crowds out the ability to trust strangers, trapping economic coordination and human development at a deeply local, tribal scale.
The Technological Leap
Before money, humanity was trapped between two dead ends. We could choose barter, which offered zero trust and infinite friction. Or we could choose kinship, which offered high trust but severely limited scale.
Bilateral trust—knowing and trusting the specific person you are trading with—simply became too expensive to produce as societies grew.
Money was the technological breakthrough that bridged this gap. It allowed humans to substitute the expensive, unscalable trust of kinship for a cheap, highly scalable institutional trust. When you accept a dollar bill, a gold coin, or a digital transfer from a stranger, you do not need to trust the stranger. You only need to trust the token.
But how did this leap actually happen? It wasn’t designed by a visionary or decreed by a king’s master plan. Instead, money was an accidental invention. It emerged from the bottom up, sustained by stable local equilibriums where substituting a token became easier than finding a perfect barter match. Once stumbled upon, this system spread through evolutionary fitness at a societal level. Societies that adopted this scalable trust out-cooperated, out-traded, and out-grew those that remained trapped by the limits of the Kinship Tax.
Follow-up
This post has focused on why money is as useful as it is to humans, and why that usefulness is best described as an extension of trust. This falls into the Technologies of Trust series. While this first post updates on the value and concept, others will deal with history and deeper meaning.