Sometimes the obvious demands restatement: Iran will decide whether it acquires a nuclear weapons capability. The US, Europe and the broader international community can seek to influence its choice. They can impose costs and offer incentives. They can probably delay Iran?s programme. But ultimately the decision will be taken in Tehran.

Much of the present debate starts from a different premise. It offers its audience a binary choice between coercive diplomacy, sanctions and military force on one side and a dangerous regime equipped for nuclear terrorism on the other. Thus John McCain, the Republican senator and contender for the US presidency, says that the only thing worse than another Middle East war would be a nuclear Iran. These, though, are not necessarily alternatives. American bombing raids might well solidify Tehran?s nuclear intent. Economic sanctions could have the same effect.