Will China emerge as a high-income country still ruled by a communist party state? If China were to achieve this, it would transform a world in which all large, high-income countries are currently democratic. It would reshape the global balance of power, not just economically and militarily, but also politically and ideologically. This is what President Xi Jinping expects to happen. But how likely is it, in fact?

Today, China is not quite exceptional. True, the number of countries ruled by a party that calls itself communist is far smaller than it was before 1991. Yet there remain a few others, notably Vietnam. True, too, it has achieved four decades of staggering economic growth. Yet it is still a middle-income country, ranked by the International Monetary Fund at 75th in the world, in gross domestic product per head at purchasing power parity - a little behind Mexico and Thailand.