For other commentators, the value of money is established because money is accepted. But why is it accepted? Well, because it is accepted!

The demand for a good arises because of its perceived benefit. For instance, people demand food because of the nourishment it offers them. The difference with money is that people demand money not for direct use in consumption but in order to exchange it for other goods and services. According to Murray Rothbard,

Money, per se, cannot be consumed and cannot be used directly as a producers' good in the productive process. Money per se is therefore unproductive; it is dead stock and produces nothing.

Money is not useful in itself, but rather because it has an exchange value—it is exchangeable in terms of other goods and services. Money is demanded because the benefit it offers is its purchasing power. Consequently, for something to be accepted as money, it must have a preexisting purchasing power.

So, how does money originally acquire purchasing power?

In his writings on this subject, Austrian economist Carl Menger raised doubts about the soundness of the view that the origin of money is government proclamation. According to Menger,

Money is not an invention of the state. It is not the product of a legislative act. Even the sanction of political authority is not necessary for its existence. Certain commodities came to be money quite naturally, as the result of economic relationships that were independent of the power of the state.

He further stated,

An event of such high and universal significance and of notoriety so inevitable, as the establishment by law or convention of a universal medium of exchange, would certainly have been retained in the memory of man, the more certainly inasmuch as it would have had to be performed in a great number of places. Yet no historical monument gives us trustworthy tidings of any transactions either conferring distinct recognition on media of exchange already in use, or referring to their adoption by peoples of comparatively recent culture, much less testifying to an initiation of the earliest ages of economic civilization in the use of money.

The Difference between Money and Other Goods
To recap, the demand for a good arises from its perceived benefit. For instance, people demand food because of the nourishment it offers them. With regard to money, people demand it not for direct use in consumption, but in order to exchange it for other goods and services. Money's usefulness is its exchange value—it is exchangeable in terms of other goods and services. The benefit it offers is its purchasing power (i.e., its price).