Fraggle Nails It in the Comments.

left a new comment on the post Money:
The question posed on the thread was: "If money is a “measure of indebtedness”, who is indebted to who when gold coins are used as money? The answer is “no one”. And the same goes for all commodity monies."
Fraggle replied thusly:
Wrong.
The extent to which a commodity is *used and treated as money* is the extent to which it is *no longer a commodity*. It's all about the reason why it is accepted in trade. An item or token is money when it accepted because of the expectation that others *in general* will accept it in trade.
When someone accepts something as money rathen than as a commodity, then for them the transaction is not actually complete, because they haven't yet got what they actually want. What they have is a general claim on stuff.
This claim is what money is a measure of and is equal and opposite to others' de facto obligation to give actual stuff for something that they do not want in and of itself, and it doesn't matter what that something is, nor what it *used* to be for.
Exactly. It's not difficult, is it?