A currency can arise from any fungible, tradable, generally-durable commodity that the bulk of society decides to accept as being worthwhile. In prisons cigarettes often fill that role; in pre-agrarian hunter gatherer groups it's often little baubles like shells. Government isn't necessary for this, but social contract is. You need to have enough faith that your neighbor will accept the currency to accept it yourself.

Cryptocurrencies have the advantage that they can be spent worldwide, instantaneously, with little friction, while most commodities require that you be physically present to exchange them. They're also significantly easier to store and more resistant to garden-variety theft, as long as they're secured by passphrases. But they exist in the uncanny valley of requiring electricity and Internet. It is fairly unlikely that the government collapses and yet you still retain always-on electricity and Internet. What will you use to pay the electric company, and how do you enforce the contract that they keep providing you power?

There's perhaps an interesting role for a digital cryptocurrency that does not require always-on connectivity, eg. something that can be carried over SneakerNet for local transactions, and then automatically syncs up with the global system when the community regains Internet connectivity. In actual conflict zones today, people seem to get intermittent electrical & Internet connectivity, eg. the electricity will come on for an hour a day with rolling blackouts, and then you try to get everything charged in that one hour. And there are enough solar installations out there that several communities are likely to retain significant power even in the event of a societal collapse. But current crypto's consensus mechanisms aren't built for intermittent connectivity: you'd need to build and design something that is eventually consistent, where a weeks-long fork does not result in two competing cryptocurrencies.

> A currency can arise from any fungible, tradable, generally-durable commodity that the bulk of society decides to accept as being worthwhile. In prisons cigarettes often fill that role; in pre-agrarian hunter gatherer groups it's often little baubles like shells. Government isn't necessary for this, but social contract is. You need to have enough faith that your neighbor will accept the currency to accept it yourself.

Are cigarettes really currency in this case? Aren't they more like one of many possible barter units? Can't you also price things in ramen packs in prison?

Similarly, I thought the sea shells thing had been sort of debunked. In that scale of society you don't need currency, you know the guy. David Graeber summarizes this rather intuitively. Why would you need to give a guy a sea shell in a "hunter gatherer group"? You're gonna see him every day of your life and everyone is gonna know/remember he owes you one. It would be like giving your sibling a sea shell because you did them a little favor or something. It doesn't actually happen because it would be a complete waste of time, just actually return the favor next time. I believe the sea shell thing is more like a gift, rather than a currency. People liked giving each other shells. They didn't think of it as currency.

I think on most modern theories, currency really comes about from conquest. The idea is as you expand these informal IOUs are not enough. You don't want to have to lug around ramen packs or cigarettes. So at the point of a sword or w/e you say hey take this coin and give us food and then you honor the coin enough and people trust it, not because it's "fungible, tradable, generally-durable commodity that the bulk of society decides to accept as being worthwhile" but because if you don't accept it the government will kill you.

That's basically what it says on American money. "This note is legal tender for all debts, public and private". So sure a business can refuse you service, that's a separate issue. But if you have a debt in the United States and you try to give them US dollars and they refuse now they are breaking the law, aka inviting the wrath of the state. So everyone uses dollars because the last thing anyone wants is to be in debt and think a pack of ramen is gonna work and they just get to say no thanks cigarettes for me please.