1. Cooperation produces what we need to live and cooperation requires accurate communication.
2. Spoken language communicates well short distances. Writing communicates well longer distances. Money communicates the longest distances, but not well.
3. Money's value is undefined. Each of us must estimate its value from many wages, prices and incomes in order to get a general sense of how much our money is worth. A dollar is worth a lot more to a poor person than it is to a billionnaire. That's the problem.
4. The solution is to define the unit for money like the unit for meter whose length is the same everywhere in the world. Then a free market can also be a fair market.