Thanks again for well-focused questions and comments. Here we are concerned with why government “fiat”currency is accepted. The short answer was that “taxes drive money”: since you have a tax liability that must be cleared by delivering the government’s own currency back to government, you want to obtain government currency. So in that sense, it is the tax liability that drives the desire to obtain government currency.
I did leave a couple of teasers, which some touched on in their comments. First, does it have to be a tax? Clearly the answer is “no”: if government imposes a fine on you in the form of five Dollars, you need five Dollars in the form government is willing to accept to pay your fine—sovereign currency. Until the 20th century, taxes were relatively less important; what mattered more were fines and tithes and fees.
To go further, let us say government monopolizes the water supply (or energy supply, or access to the gods, etc); it can then name what you need to deliver to obtain water (energy, religious dispensation, etc). In that case, if it says you must obtain a government IOU, then you want government IOUs—currency—to obtain water in order to avoid death by dehydration. In early 19th century England, almost all activities necessary to keep your family alive were illegal by dictate of the crown. You had to pay a fine after you killed game to feed your family. You needed the crown’s currency to pay the fine—hence “fees drove money”. You get the picture.
All you need to drive a currency is a more or less involuntary obligation to deliver the currency—and that can be a tax, fee, fine, or even religious tithe. Or a payment to obtain water or any other necessity. We can go into this later, but at UMKC students need buckaroos to pay a “tax” to pass their courses—that drives the buckaroo currency—it creates a demand for buckaroos (the sovereign currency at UMKC).
That answers the question: yes it is not enough to impose the obligation (fee, fine, tax); the obligation must also be enforced. A tax liability that is never enforced will not drive a currency. A tax that is only loosely enforced can create some demand for the currency, but it will be somewhat less than the tax liability for the simple reason that many will expect they can evade the tax.
We can next move on to the second teaser: why would those who do not have tax liabilities also be willing to accept currency?
That leads us to the Tobin, “snowball” point: if some segment of society owes the tax (or fee or fine) denominated in the currency, others will accept it. Note this is not an infinite regress argument. It is the tax standing behind the currency. But it is not necessary for every individual to owe the tax.
Let us say that Bill Gates owes $1.5 trillion in taxes. I’d be happy to accept Dollars since I know Gates will accept them when I purchase Microsoft software. And that explains why foreigners want dollars—not because they owe taxes, but because a sufficient number of Bill Gates do.
From inception we know that if the total tax liability in dollars is, say, $100 billion, the taxpayers will want a minimum of $100 billion. (How much more? $120 billion? $180 billion? We will investigate that later.) Government can spend into the economy at least that amount.
How much will the Dollar be worth? Well, that depends on what must be done to obtain it. We will have much more to say about that in coming weeks.
A commentator did hit on this point: what if the tax liability is too low? Let us say the tax liability is $100 billion but government tries to spend $1000 billion. This is ten times what the taxpayers need to cover their liabilities. It is possible—even probable—that government will not be able to find takers for the $1000 billion. It can bid the price it is willing to pay (for labor, finished output, or resource inputs) up, but still find no takers. We could register “inflation” and still find government cannot spend as much as it wants.
A better solution—obviously—is to raise the tax liability toward $1000 billion, rather than to increase the price government is willing to pay. Again, that is something we will come back to, but it also sheds some light on what determines the value of the currency. As I said last week, we need to separate the willingness to accept currency from the value of the currency. Raising the tax liability will increase the desire to obtain currency although that does not tell us exactly how much the value of currency (in terms of labor or other resources) will rise.
Valuing something like a bridge is very difficult—especially if we are talking about a bridge already in place. Fortunately, it is also a question that is not very important, so long as the bridge is public—not owned by some profit seeking entity. There really is very little reason to value public infrastructure once it is in place, except perhaps in terms of all the pleasure it provides to the population. That is probably something that cannot be and should not be measured in money terms.
But, yes, raising the tax liability while holding government issue of the currency constant is likely to lead to what we might call unemployment: those willing to work to get the currency in order to pay taxes, but who cannot find work or demand for output to obtain the currency.
We will later go through the accounting to answer the question raised by a commentator: what about the reserve effects of tax payments? But, briefly, yes, paying taxes will all else equal reduce outstanding bank reserves. In practice, if the central bank targets overnight interest rates, it will replace lost reserves if they were desired or required—by lending at the discount window or through open market purchases of treasuries.
There were several questions/comments that were not comprehensible to me: what about interest, which requires one to repay more than what is owed. I do not see the relevance to this week’s topic. What about issuing money with no offsetting debt? Well, all money “things” are IOUs hence are debts, hence there is no possibility of issuing money that is not a debt. What about socio/political ramifications of who pays the tax? Yes very important, but I do not see the relevance to the topic at hand.

OK I hope I have covered the main comments and questions. More next week.