I have to disagree with Matt Forstater about what defines "fiat currency." He implies that it is essential that it involve liabilities. But this seems exactly backwards. Under a gold standard, paper money was a liability: it was exchangeable by right into gold coin. Fiat money differs from earlier paper money in that it is not exchangeable by right into something else. That older, post-gold-standard U.S. paper money continued to say "payable to the bearer on demand, the sum of . . ." was just an artifact of its prehistory as a parasite on a metallic standard. Recent paper money drops this pretense. It is similarly a pretense for the Federal Reserve to treat its banknotes as liabilities. Yes, the aluminum disks of the capuchin moneys do not involve liabilities, but in no practical sense does a U.S. dollar bill either. But aside from that, are the monkey's involved in barter when they use the disks? Only if all exchanges using gold coin were also barter. One can easily define barter in such a way to make that true. But the moneyness of gold coins comes from a social property that is worth distinguishing from barter. Gold can be the source of direct utility (in jewelry or electrical circuits), but to most holders of gold coin, it is valuable because it is accepted as valuable by other people, and therefore an excellent intermediary in transactions. It is the presence of such an intermediary that distinguishes monetary exchange from barter. The gold standard had this property (typical money was not a liability); the gold-(or silver-)backed paper money system had it (typical paper money was a liability); and the current fiat-money standard has it (typical money is not a liability). The monkeys' aluminum disks presumably are not a source of direct utility, but are held because they facilitate exchanges for things that are sources of direct utility: that looks like fiat money. Kevin Hoover