"This, you might say, is how the notion of money-as-a-common-unit arises under the Law, when mortals meet and deal with each other. The world begins with farms and scythemakers," Keltham has picked up that scythes are involved in farming, "so why does it need money? Let farmers barter corn for scythes, let scythemakers eat some of the corn and barter other corn for metal, let the metalmaker barter metal for shoes - don't tell me that's not the right trade pattern, Tonia, just pretend I said something sensible, please."
"Why not just trade things you have for other things you want? Why try to price everything in the same units everywhere? Who's to say that wouldn't just cause everyone to make weird trades they wouldn't have made, would have been wiser than to make, if bartering things directly?"
"But if people are in general trading in ways that don't let you extract lots of resources from them, they will be acting as if you could price everything in corn, or everything in pounds of iron, and have their trading patterns mostly make sense in those terms. You won't be eliminating a lot of useful complexity and extra details that mattered, when instead of having all the local patterns of bartering ratios, you instead try to price everything in corn. You are not holding up a mirror to life, and cutting off the pieces of life that don't fit; everything does fit into the mirror. It's safe to do the thing that lets somebody work out a glance a ratio between shoes and scythes, without having to envision in detail how relatively useful shoes and scythes will be to them."
"That's what justifies, you might say, the approach of trying to weigh a book about rare magic items, and a book about spell design, relative to one another, by weighing both of them in some common unit, and not just comparing them to each other."
"Should that common unit be gold pieces, or minutes of our time? The minutes of our time are, from one perspective, the most natural way to think about the resources that we have; almost anything else we want, that we can try to get, is going to burn some number of minutes of our time, and maybe some other resources too, but always the minutes. As for money, you can always convert your time into that; even if your job saturates in a way that doesn't let you voluntarily work an extra hour or an extra day, you could trade your time for money elsewhere, by finding an employer who just needs an hour of work from somebody, even if that pays less well... Actually now that I'm arguing this out loud I have a sudden worrying sensation that in Golarion it's not actually going to be possible for lots of people to trade their time into money at any reasonable exchange rate."
"Anyways, in Civilization, where you can convert between time and money, the common wisdom is that you should learn to value everything in terms of money, rather than minutes of your personal time. Why? Because that way you can, without an extra mental translation step, tell other people your prices, and understand what their prices are. Time is the personal resource closest to us, but society's shared unit of wantingness is the way we interact with everything else, and so the common wisdom is that we'll all end up better off if we think in society's units."
"Of which it is said in dath ilan, 'money is the unit of caring' - with further implications such as, for example, that if you're weirdly reluctant to spend any money on something, you probably don't care about that thing very much. Though the proverb loses something because Civilization's word for society's common unit for pricing, 'unit-of-account', is one of three different Baseline words I've found so far that all translate into Taldane's word 'money'."