Money is a product of law, and if you don't think that is "real" enough just try not paying your taxes in the denomination your government demands. You will find quickly that the government's demands are backed up with its ability to separate you from any "real" property or resources you own, even up to your personal freedom (jail time).

The quest for something of tangible substance to denote value in our commerce is as old as commerce itself, but a modern economy requires a universal measure with which it can divide labor and facilitate storing excesses. Barter satisfies neither of those, so it has never been part of any modern economic system. That measure of value, from the earliest records in history, has been what the ruling government has decreed as its standard in satisfying tax obligations.

You can trade your wares in barter or seashells as long as you can provide the currency of the issuing government when the tax man comes around. If the currency-issuing government provides enough excess currency (deficit spending) it is most likely that currency will be adopted as the standard for commerce as well.

This power over the purse provides an extreme amount of control over the function and order of a society. The currency-issuing government never "needs" its own currency back to facilitate its spending, but it does need us to need its currency to be able to assure the productivity and full employment of its economy. Most of the precarity the working class suffers is not the result of any economic factor, but a conscious political decision by the country's leadership desiring to cater to the whim of the donor class.