If merely having an exchange value in the future made anything money, then we could only buy or sell things that lacked future exchange value: otherwise, those things would be the money with which we buy them or for which we sell them, rather than what we buy with money or sell for it. Many things have once represented money, but not only because of their future exchange value (otherwise, almost anything would always be money, leaving us just a few, quite uninteresting things to buy - and serious problems in choosing the money to buy them with).
Not just commodities can be bought and sold, money can be bought and sold too. That's why there's a giant market of currency exchange. You're creating another false dichotomy that money and commodities are always entirely separate things (sometimes they are, but not always). The other false dichotomy is that money and credit are separate things. In reality, its blended together on a spectrum: pure credit/currency on one end, and commodities with no exchange-value on the other.
Let me give you an example from my book
Representational Monetary Identity (
http://omniequivalence.com/money-as-multiequivalence/):
It was you to say that merely having a future exchange value made anything money.
Still, gold also has a use value independently of being money, as does cattle, silver, and salt. They are also useful "regardless of whether or not I trust you," and even so they can be - as once were - money.
Its having a future exchange-value based on trust which makes something a currency. Not "future exchange-value based on use", which is a total misuse of the term exchange-value. future exchange-value (the gold) is a separate thing from future use-value (the knife).
Neither trust nor utility can give anything an exchange value, whether monetary or not: trust is merely a requirement for social interaction in general, and utility, for exchange value in general and monetary value in particular.
But we do agree, having a use-value does not preclude something from also functioning as money. Commodities can have a dual-function as both currency and as commodity (again, in the real world, its a complex blend). The point is that, as a currency, its exchange-value is derived separately from its use-value. The exchange-value comes from the network of trust among people who will accept it as payment, even if have absolutely no intention of using it themselves (just an intention to exchange it again in the future).
Exchange value is never "derived from" utility: although a commodity must be useful to have exchange value, its exchange value does not originate from its utility. Likewise, although we must trust each other to buy from and sell to each other, the exchange value of our commodities and money does not come from our trusting each other (otherwise, the more we trusted each other, the more valuable our commodities and money would become).
(if it were a ceremonial knife made of precious metal, then we could assume it would have additional exchange value above and beyond its cutting utility, and the scenario would be different).
So its metallic utilities would make it useless, then credit, hence money?
No, its ceremonially-precious quality would give it exchange-value (derived from the trust and agreement that it is precious). That is entirely separate from its utility as a cutting tool (its use-value).
The question was: how its metallic properties could enhance its exchange value? In your terms: why those properties would affect our "agreement" on its exchange value? Do not objective properties affect the exchange value of things? Otherwise, would it not be just a coincidence that some things are consistently more expensive than others?
It is not a matter of just "presuming" things, but rather of explaining how things are the way we "presumed" them to be: the circularity arises from trying to explain, by using your own argument, how money and credit could be the same.
Okay, credit/IOUs have value based on trust, that should be obvious (an untrusted IOU is worthless). Money/currency have value based on exchange. And that exchange-value is always in flux, clearly, the price of gold and bitcoin are constantly changing. Changing based on what?
Now we are talking. Take more time on the question before trying to answer it: this is not an easy one.
Based on the trust that it can be taken to the market and exchanged at x price in the future, in other words, that it can serve as a "good-as-gold" "buyer-owes-u" x in the future. If that trust collapses, the price collapses.
In my example above, those three owners can choose a fourth commodity to represent money
just in the context of that particular exchange. In this case, money would need not be valuable in the future: the only trust required would be that of the owners in each other (that they would not kill - or steal - each other, etc).
Physical gold is just a token which measures the credit backing by the gold market. So instead of an "i-owe-u" its a "gold-market-owes-u". And obviously a "gold-market-owes-u" is only as valuable as the collective trust in the gold market.
So the more we trust gold to have an exchange value in the future, the more valuable it will be?
One thing is to trust
more on the future monetary value of gold; another is to trust
on more monetary value of the future gold.