This U.S. election campaign is being billed as a battle of big ideas. That is a good thing. But it is a shame that the fight is not being waged in the 21st century.

In choosing Representative Paul D. Ryan as his running mate, Mitt Romney swapped his Massachusetts pragmatism for a proudly ideological commitment to limited government. The Democrats, by contrast, believe in the essential role government plays, and are willing to raise taxes, at least on the rich, to pay for it.

This a clear and important battle line in the United States. But the argument over the size of the state comes with little regard for the very particular economic realities of this era. Like generals fighting the last war, U.S. politicians are solving the economic challenges of the past century.

That is a problem because we are living at a time of deep and fast economic change. The intuitive sense that the economy is becoming less predictable and less secure is right. Thanks to globalization and the technology revolution, the nature of work, the distribution of the rewards from that work and maybe even the economic cycle itself are being transformed.

But one would not know it from the U.S. political debate, whose familiar melodies of small state versus large state, higher taxes versus lower taxes and the importance, or not, of balancing the budget could have been played in any decade since World War Two.