When you lend somebody money, they usually have to pay you for the privilege. That has been a bedrock assumption across centuries of financial history. But it is an assumption that is increasingly being tossed aside by some of the world’s central banks and bond markets. A decade ago, negative interest rates were a theoretical curiosity that economists would discuss almost as a parlor game. Two years ago, it began showing up as an unconventional step that a few small countries considered. Now, it is the stated policy of some of the most powerful global central banks, including the European Central Bank and the Bank of ... (full story)