The framework agreement announced this week between Iran and the major powers isn't a formal accord on Iran's disputed nuclear program but rather a broad statement of principles that eventually could form the basis for one. Months more of hard bargaining will be needed to work out the details of how those principles translate into a final agreement acceptable to both sides. But the fact that negotiators appear to have cleared this first major hurdle is a hopeful sign that the goal of preventing Iran from developing nuclear weapons through diplomatic means is achievable.
The basic outlines of the deal call for Iran to shut down all but about 5,000 of the 19,000 centrifuges it has...