Overview

In economics, a medium of exchange is any item that is widely accepted in exchange for goods and services. In modern economies, the most commonly used medium of exchange is currency. Most forms of money function as media of exchange, including commodity money, representative money, cryptocurrency, and most commonly fiat money. Representative and fiat money exist in digital form as well as physical tokens, for example coins and notes.

Economists, such as William Stanley Jevons, had assumed that exchange media would have arisen in antiquity as awareness grew of the limitations of barter. The form of the medium of exchange follows that of a token, which has been further refined as money. A medium of exchange is one of the functions of money. The medium acts as an intermediary instrument, the use of which can be to acquire any good or service and avoids the limitations of barter; where what one wants has to be matched with what the other has to offer.

However, there is little evidence of a pre-monetary society in which barter is the primary mode of exchange; instead, such societies operated largely along the principles of gift economy and debt.

Credit as the origin on money

In his book Debt: The First 5,000 Years, anthropologist David Graeber argues against the suggestion that money was invented to replace barter. The problem with this version of history, he suggests, is the lack of any supporting evidence. His research indicates that gift economies were common, at least at the beginnings of the first agrarian societies, when humans used elaborate credit systems. Graeber proposes that money as a unit of account was invented the moment when the unquantifiable obligation "I owe you one" transformed into the quantifiable notion of "I owe you one unit of something".

In this view, money emerged first as credit and only later acquired the functions of a medium of exchange and a store of value. Graeber's criticism partly relies on and follows that made by A. Mitchell Innes in his 1913 article "What is money?". Innes refutes the barter theory of money, by examining historic evidence and showing that early coins never were of consistent value nor of more or less consistent metal content. Therefore, he concludes that sales is not exchange of goods for some universal commodity, but an exchange for credit. He argues that "credit and credit alone is money".

Anthropologist Caroline Humphrey examines the available ethnographic data and concludes that "No example of a barter economy, pure and simple, has ever been described, let alone the emergence from it of money; all available ethnography suggests that there never has been such a thing".

Economists Robert P. Murphy and George Selgin replied to Graeber saying that the barter hypothesis is consistent with economic principles, and a barter system would be too brief to leave a permanent record. John Alexander Smith from Bella Caledonia said that in this exchange Graeber is the one acting as a scientist by trying to falsify the barter hypotheses, while Selgin is taking a theological stance by taking the hypothesis as truth revealed from authority.

Barter as the origin of money

In a barter transaction, one valuable good is exchanged for another of approximately equivalent value. William Stanley Jevons described how a widely accepted medium allows each barter exchange to be split into three difficulties of barter. A medium of exchange is deemed to eliminate the need for a coincidence of wants.

Want of coincidence

A barter exchange requires each party to a transaction to have something the other desires. A medium of exchange removes that requirement, allowing an individual to sell and buy from various parties via an intermediary instrument.

Want of a measure of value

A barter market theoretically requires a value being known of every commodity, which is both impractical to arrange and impractical to maintain. If all exchanges go 'through' an intermediate medium, such as money, then goods can be priced in terms of that one medium. The medium of exchange allows the relative values of items in the marketplace to be set and adjusted with ease. This is a dimension of the modern fiat money system referred to as a "unit of account."