The value in exchange of commodity money is largely based on the commodity's value in use. In fact, the earliest forms of money were commodities that provided value in use to virtually everyone in an economy, such as grains for food and animal skins for clothing. For example, in the early eons of civiliaation, people were willing to accept bushels of grain in trade for another good because they were hungry, because the grain had value in use, NOT necessarily because they planned to use the grain to buy another good, NOT because the grain had value in exchange.

However, knowing that EVERYONE was willing to trade for grain gave it value in exchange. Because people couldd trade the grain to others, they were willing to accept grain in payment even when they were NOT hungry, even when the grain. did not provide them with value in use.

The value in exchange of fiat money is based exclusively on an item's widespread acceptance AS MONEY. In the modern world, people accept fiat money in payment because EVERYONE accepts fiat money in payment. Continued acceptance of fiat money rests largely with the authority responsible for issuing the money, usually government. If the issuing government remains healthy, trustworthy, and responsible, then the money that it issues continues to be accepted as payment. A primary way that government maintains the "official" status of money is to accept it in payment for taxes. Usually, not always, but usually, whatever item the government is willing to accept as payment is good enough for the rest of the economy. Such acceptance gives the item value in exchange.