Everything you ever wanted to know about the why of money can be found here, in “A Brief History of Money”, from the ieee Spectrum. It is, of course, a very nutshell overview, because if it were simple in any way then we’d all be rich. The biggest takeaway is the different way that the value of paper money is explained, which gives a bit better perspective on why having the Federal Reserve isn’t such a bad thing, provided inflation is controlled and money supplies remain liquid. One thing I didn’t know: electrum coins from Lydia are the first modern monetary system in history. That is, if we can trust Herodotus, but I thought money would have been much older.