currency was made to hold value, and a medium of exchange. an early bartering system could not be effective because stuff (especially food) decays with age, and doesn't hold its value indefinitely. it is hard to get an exact match of what both parties are asking for in a bartering system, because maybe someone doesn't feel his grain is worth 2 chickens, but 2.5 chickens. but how the fuck do u get a 1/2 chicken?