'On Dec. 19, Mr. Erdogan explained that he is crafting policy on his interpretation of the Quran’s commandment prohibiting paying interest on money: “They compl

'On Dec. 19, Mr. Erdogan explained that he is crafting policy on his interpretation of the Quran’s commandment prohibiting paying interest on money: “They complain we keep decreasing the interest rate. Don’t expect anything else from me. As a Muslim, I will continue doing what our religion tells us. This is the command.” That single, disastrous remark caused the lira immediately to drop 12%. The realization that Mr. Erdogan’s policies were based on the live commands of the Quran, not the theories of a dead American economist, spooked the market. Mr. Erdogan’s conviction about interest rates has terrible implications for Turkey. Protests and hunger are spreading, and the country could go the way of Venezuela. Duke economist Timur Kuran said the coming chaos gives Mr. Erdogan and his minions “an opportunity to declare emergency rule and stay in power despite their rising unpopularity.” Mr. Erdogan’s “what our religion tells us” statement shows a subservience to medieval notions about finance, no matter the harm they cause. But medieval religious regulations don’t mix well with modern finance—or with almost anything. Muslim success in the modern world requires a reconsideration of Islamic laws in light of current circumstances. Quranic regulations could be interpreted to allow for reasonable interest payments while banning usurious interest.'