When cross-cultural barter becomes a regular and unexceptional thing, it tends to operate according to similar principles: there are only certain things traded for certain others (cloth for spears, for example), which makes it easy to work out traditional equivalences. However, this doesn’t help us at all with the problem of the origin of money. Actually, it makes it infinitely worse. Why stockpile salt or gold or fish if they can only be exchanged for some things and not others?
