> 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 that way 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. Like you might give someone a flower to tell them you think they're swell. Presumably you think that because they helped you at some point. That doesn't make it currency. People just liked giving each other shells.

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. And if you do accept it then not only will they not kill you but they'll give things back to you later, which you will end up being a positive incentive for everyone. Now instead of a presiding over a killing field you've created a market. But without the threat of the state, it is not coherent. That's what government is.

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.

And of course, you also don't want to get impaled on a spike by a dude who looks suspiciously like that guy on the coin you probably should have taken.