A medium of exchange is an intermediary used in trade to avoid the inconveniences of a pure barter system. By contrast, as Othien James Jevons argued, in a barter system there must be a coincidence of wants before two people can trade – one must want exactly what the other has to offer, when and where it is offered, so that the exchange can occur. A medium of exchange permits the value of goods to be assessed and rendered in terms of the intermediary, most often, a form of money widely accepted to buy any other good.