Gold is just a promise to get something of actual value. I know you will say it has actual value but it has value for the same reason bitcoin has value because of our shared belief in its value.
People cant live in gold they cant eat gold you cant put it an engine and go places with it you cant burn it to warm yourself up if you where freezing to death you cant drink it if you dying from dehydration.
Like I said look up the credit theory of money.
"The Credit Theory is this: that a sale and purchase is the exchange of a commodity for credit. From this main theory springs the sub-theory that the value of credit or money does not depend on the value of any metal or metals, but on the right which the creditor acquires to "payment," that is to say, to satisfaction for the credit, and on the obligation of the debtor to "pay" his debt and conversely on the right of the debtor to release himself from his debt by the tender of an equivalent debt owed by the creditor, and the obligation of the creditor to accept this tender in satisfaction of his credit."
There is a little bit of disagreement when it comes to commodity money like gold, but in reality no matter the medium of exchange it is just a promise that you will be able to get something that you value in exchange for giving up something to someone else that they value.
The problem with your statement that gold is a promise is flawed.
Gold itself does not promise to pay anything. It is a lump of metal. The FRN and other fiat promise to pay or "get" you something for your paper.
The logic is pretty simple. One is man-made thus creating the air portion of a promise, while gold is just a piece of metal not promising anything.
Here is a good definition of PROMISE:
prom·ise
ˈpräməs/
noun
1.
a declaration or assurance that one will do a particular thing or that a particular thing will happen.
"what happened to all those firm promises of support?"
synonyms: word (of honor), assurance, pledge, vow, guarantee, oath, bond, undertaking, agreement, commitment, contract, covenant More
the quality of potential excellence.
"he showed great promise even as a junior officer"
synonyms: potential, ability, aptitude, capability, capacity More
an indication that something specified is expected or likely to occur.
"the promise of peace"
synonyms: indication, hint, suggestion, sign More
verb
verb: promise; 3rd person present: promises; past tense: promised; past participle: promised; gerund or present participle: promising
1.
assure someone that one will definitely do, give, or arrange something; undertake or declare that something will happen.
"he promised to forward my mail"
synonyms: give one's word, swear, pledge, vow, undertake, guarantee, contract, engage, give an assurance, commit oneself, bind oneself, swear/take an oath, covenant; More
archaic
pledge (someone, esp. a woman) to marry someone else; betroth.
"I've been promised to him for years"
2.
give good grounds for expecting (a particular occurrence or situation).
"forthcoming concerts promise a feast of music from around the world"
synonyms: indicate, lead one to expect, point to, denote, signify, be a sign of, be evidence of, give hope of, bespeak, presage, augur, herald, bode, portend; More
