People’s Trust is what makes Fiat FRN Promissory Notes Elastic Money!

Fiat FRN Promissory Notes? Crucially, people trust that the value of money will endure over time with the good faith of the US Government.
The Difference Between Commodity Money and Fiat Money

Historically, as trade increased through the centuries, commodities or intrinsically valued money such as lawful gold and silver were used in most countries.