The Constitution reflects a hostility to this idea because it tends to restrain trade, Stevens writes, and nothing Congress has done since to define patent law can be seen as encouraging government-sanctioned monopolies on processes alone.

FORBES: The Bilski Ruling That Almost Was

If rates were raised high enough to restrain mortgage lending, they could also jeopardise the broader economy, especially since household and corporate debt together add up to as much as 200% of GDP.

ECONOMIST: Ways to stop boom turning to bust

Most of its deficit reduction has come from higher revenues, but the government has tried to restrain expenditure: federal spending has risen by around 1.5% a year since 2004.

ECONOMIST: Germany's tax debate