Imagine Gilligan’s Island without the Howells and their paper dollars. Without money, commodities exchange directly: coconuts for fish, fish for bamboo, etc. But even with barter, some commodities are more “marketable” than others. Perhaps one of the castaways might eventually buy one of the Professor’s books, but they will more often purchase Mary Ann’s coconut cream pies — or the coconuts themselves. Coconuts are more marketable than books.

Over time, the commodity that is most marketable becomes popular for indirect exchange: the Skipper trades his fish for Ginger’s decorative shells, not because he wants shells, but because he knows he can trade them for Gilligan’s coconuts. The price of a commodity is its exchange ratio for the most marketable good, e.g., 12 shells per coconut. The value of the shell money is based on the goods it traded for yesterday — since we can’t know what prices will be today. Right now, the Skipper is willing to trade one of his fish for two coconuts, and he knows that Gilligan was recently willing to trade his coconuts for a dozen shells each, therefore the Skipper wants to price his fish at two-dozen shells each: enough to buy two coconuts. Prices can change from day to day, but today’s new prices will be based on the prices of other things yesterday. —B. K. Marcus —The Monetary Economics of Thurston Howell III  (Ludwig von Mises Institute)