Fungibility

Key points

• Fungibility is the property of an asset whose units are indistinguishable from one another, holding the same value and function.
• A ten-real bill is equivalent to any other ten-real bill; it is this loss-free interchangeability that defines a fungible asset.
• In the crypto world, coins and most tokens are fungible, while non-fungible tokens represent unique, non-substitutable items.

What is fungibility?

Fungibility is the characteristic of a good whose units can be exchanged for one another without any difference. Money is the classic example: one unit is worth exactly the same as another and can replace it in any situation. This uniformity is what makes an asset practical as a medium of exchange and as a unit of account.

How it works

An asset is fungible when it doesn't matter which specific unit you have, only how much you have. When you receive crypto in a stablecoin, for example, it makes no difference which units arrived: all of them are identical in value and use. This allows you to add, divide, and transfer freely, without needing to track the identity of each unit.

The opposite is non-fungibility. A non-fungible token carries its own identifier that distinguishes it from all others, like a numbered ticket or a specific work of art. In that case, each unit is unique and cannot simply replace another, because what matters is precisely the identity of that unit.

In practice, fungibility also depends on perception: if certain units of an asset are seen as suspicious because of their history, they may be treated differently, which reduces fungibility in practice. Even so, for most payment uses, the fungibility of major stablecoins remains solid on a day-to-day basis.

Why it matters

Fungibility is what makes an asset usable as money. For payments, it is essential that one unit of a stablecoin be worth the same as any other, without the history of each one changing its value. It is this uniformity that allows values to be quoted, settled, and reconciled simply. It is also what lets wallets and systems treat every unit as equivalent, without needing to track the origin of each fraction received.

Risks and limitations

Since the history of each unit is recorded on the blockchain, fungibility can be affected when units linked to illicit activity start being flagged or refused. This creates a tension between the transparency of the public ledger and the idea that every unit should be perfectly interchangeable.