[chiefalchemist]

Noah. That's simply not true. Lyn Alden's "Broken Money" does a couple+ chapters on the history of money. "Cross cultural" transactions are essentially. You can't have a "social contract" across sometimes conflicting cultures. Long to short, this is why we eventually ended up using gold.

[fineIllregister]

You absolutely can have a social contract across conflicting cultures. You just gave an example: commerce valuing gold is a social agreement. Another example is countries at war each other following the rules of war (not always, but even one instance makes your claim false).