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You can differentiate physical bills by serial yet we consider currency to be fungible, no?


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> Every bill has a serial number, so every bill is unique. This is what it means when money is "marked" in a police investigation, they give bills with known serial numbers to bad actors in a criminal enterprise and then recover the bills at the other end of the enterprise proving the connection.

This has nothing to do with fungibility unless a bill’s serial number affects either your ownership of the bill or whether the bill will be accepted as payment.

Fungibility is related to being indistinguishable for the purpose of economic transactions, not being physically indistinguishable.


Being fungible does not imply that something does not have a serial number or identification number. For example US dollar bills are fungible but they have serial numbers.

I see you are repeating something patently wrong and even adding some equally wrong "spice" to it, like that cash notes are non fungible by design, which is somehow "literally an inseparable part of their physical existence". This despite currency (in any form) predating the formalized concept of fungibility.

Money is fungible by every (literal) definition of the word, whether banknotes or coins. Being fungible doesn't refer to the physical aspect of being absolutely identical but to its value. Money exists to be fungible, fungibility is literally one of the big things that make money work. Going even further, money is probably one of the few things equally fungible whether new or used, and sometimes even old/outdated (think retired currency which can be converted to currency in circulation).

Whether coins or banknotes, they are interchangeable from one to another regardless of serial or the year stamped on them. And almost any other two new "identical" products are just as fungible: two loaves of bread, two planks of wood, two pencils, or two cars (not the case for used products). They're all mass produces, quasi-identical units.

And the serial numbers? They're used mainly for uniquely tracing the note and don't affect the fungibility in any way. The proof? Randomly pick a banknote every time you pay for something. If it works every time either you're the luckiest person in the world, or they're completely fungible.


That's more or less like saying dollars aren't fungible because you can check the serial number on a bill to see if it matches one that was reported stolen.

Money is fungible. Your physical dollar bill can be collected and deposited and make it possible for _another_ dollar to do something else.

Cash is kind of fungible, but not really. Every bill has a serial number, so every bill is unique. This is what it means when money is "marked" in a police investigation, they give bills with known serial numbers to bad actors in a criminal enterprise and then recover the bills at the other end of the enterprise proving the connection.

In common practice it's fungible in the sense that one twenty dollar bill is as good as another. In edge cases though it's not quite fully fungible.


Dollars have serial numbers does that mean they're not fungible? Does the author know what fungible means? Banks block transactions all the time to/from flagged sources.

I specifically took the example of a (physical) $10 bill. You can definitely tell apart two different $10 bills. They have serial numbers, for example. They're different physical objects.

They're exactly as fungible as a dollar is. A dollar with a unique serial code except every person who's had possession of this dollar has logged that serial number into a publicly visible log, even if they don't put their name next to the entry. But you can spend it like any other history tracked serialized dollar.

Ironically, money is fungible. One dollar bill is perfectly interchangeable for another dollar bill.

Fungibility has nothing to do with dollar bills and everything to do with dollars. You can't make a withdrawal from a bank after two years and ask for the same dollar bills back that you deposited.

>cash is fungible, as in each unit of currency has no ID

This may seem nitpicky to point out that it does, but since it does, I'm not sure of your point.

"A unique combination of eleven numbers and letters appears twice on the front of the note. Each note has a unique serial number"

https://www.uscurrency.gov/denominations/bank-note-identifie...


Not necessarily. Bills have serial numbers on them. They can also be marked.

By that token, neither is cash money - every bill has a unique serial number.

If 10% of $20 bills (by serial number) were not considered legal tender, then $20 bills would no longer be fungible.

The ramifications are the important part. If 10% of bills are essentially fake money, you have to verify every bill you handle, adding significant friction.


What... paper money and gold bars are non-fungible now?

I think that "tangible" doesn't quite capture the difference between an antique coin and a bill with a known serial number.

Nor are bills and coins nearly as anonymous as most people believe.

There's a reason every Euro note and US dollar comes stamped with a serial number...


The same can be true of dollar bills. A bag full of dollar bills from a drug deal is fungible with a bag full of dollars from your salary. But you can be arrested for the former, and not the latter. Dollars are fungible with dollars ($1+$1=2$), NFTs are not fungible with NFTs (1NFT+1NFT=1NFT+1NFT).
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