The principle of progressive taxation - that those who earn more should pay more in income tax - has been in retreat since the 1970s, when marginal tax rates rose so high that they were a disincentive to hard work and enterprise. But the notion that the well-off should pay a higher percentage of their income in tax than the less well-off remains both accepted and correct.

Small wonder that there is now a movement in the US Congress to correct the fact that many of the richest people - those who work in private equity partnerships and some kinds of hedge fund - pay lower tax in percentage terms than others because their wealth is accumulated in capital gains, rather than being counted as income.