Thus money is almost always something hovering between a commodity and a debt-token. This is probably why coins—pieces of silver or gold that are already valuable commodities in themselves, but that, being stamped with the emblem of local authority, became even more valuable—still sit in our heads as the quintessential form of money. They most perfectly straddle the divide that defines what money is in the first place. What's more, the relation between the two was a matter of constant political conversation. In other words, the battle between state and market, between governments and merchants is not inherent to the human condition.

Chapter Four, "Cruelty and Redemption", p. 75 - Debt: The First 5,000 Years (2011)