Remember Donald Rumsfeld's "unknown unknowns"? The US Defence Secretary used the phrase in 2003 in the context of the controversy over Iraq's weapons of mass destruction.
More than three years later the Bush administration is still paying a political price for basing its case for the liberation of Iraq on those "unknown unknowns".
It was always clear that the only way to find out whether or not Saddam Hussain had Weapons of Mass Destruction (WMD) was to topple him and seize control of his secrets. And then, when the unknowns became known, there was always the possibility that no WMDs would be found.
The case for getting rid of Saddam had little need of those "unknown unknowns". That Saddam might have had WMDs in March 2003 was neither here nor there. It was an established fact that he had used WMDs against Iran and his people on many occasions. It was also clear that a regime such as his could at any time revive a WMD programme.
At the time there were enough "known knowns" that had nothing to do with WMDs to justify toppling Saddam a hundred times over. To reduce the issue to WMDs was a mistake. The question now is whether or not the Bush administration is moving towards a new version of that mistake this time in the case of Iran?
The "unknown unknowns" in the case of Iran concerns its alleged project to develop nuclear warheads. More than three years of Gaston-Alphonse diplomacy between Tehran and the European Union trio of Britain, Germany and France, has shown that this "unknown" cannot become known through routine negotiations.
Tehran insists it is not developing nuclear weapons. The EU, however, wants it to confess that it has been lying and to provide evidence that it is not doing what it has always said it was not doing.
Now imagine what would happen if Tehran did admit that it had been lying and even produced evidence that it had stopped the programme it had always said it did not have. Would anyone trust a regime that admits it had been lying for two decades? What guarantee would there be that while admitting that it had been lying for 20 years, the Islamic Republic does not continue a clandestine programme?
There are only two ways to find out the answer for sure.
One is for the present Iranian regime to do what others, including South Africa and the Ukraine, did and invite the International Atomic Energy Agency (IAEA) to help wind down and dismantle its nuclear programme.
Another way is regime change in the hope that a new Iranian regime would either show that there was no weapons programme or, if one was found, do what South Africa and Ukraine did. Anyone with knowledge of Iranian politics would know that the present regime is unlikely to take that option. So, we are left with one option: regime change.
In that connection three questions arise. The first is whether or not there are enough "known knowns" to justify regime change in the eyes not only of the Iranian people but also of the international community?
The answer is yes.
The Islamic Republic has been and remains one of the worst violators of human rights in the world. Proportional to its population it holds more prisoners of conscience than any nation. It tops the list of nations in terms of the number of people executed, for political reasons but on false charges of moral and other "deviations".
Iran's oppressive policies, however, are not limited to the political domain but also affect cultural, religious and economic aspects of the nation's life.
All that, of course, may be dismissed as "no business of ours" by the international community. Fair enough, which brings us to the second question: what "known knowns" could be cited to justify regime change in Tehran in the eyes of the international community?
We already know about Tehran's desire to wipe Israel off the map. We also know that next week Tehran will host the largest gathering of "rejectionists" from all over the world, including leaders of Hamas, the Palestinian group that has won the elections in Gaza and West Bank. On the agenda is "an Islamic strategy to destroy the Jewish state and recover Palestine".
Another "known known" is that the terror jamboree in Tehran also includes a seminar to prove that "the Holocaust is a Jewish fabrication to generate sympathy for Israel", to quote Ayatollah Mesbah Yazdi, the regime's ideological rising star.
Well, the so-called international community may again dismiss all that as "no business of ours" because the only target appears to be Israel. But then what about what the Islamic republic is doing in Iraq and Afghanistan, to mention just two examples of Tehran's attempt at exporting its Khomeinist ideology?
Tehran has also revived contacts with dissident Shiite exiles from Bahrain and Saudi Arabia. And last December, Tehran prompted radical Shiites in Kuwait to form a party to oppose "American-inspired democratisation".
All that fits into what Interior Minister Mustafa Pour Mohammadi has described as "master plan for a pan-Shiite caliphate" covering part of the Balkans, Turkey, the Middle East, the Caucasus, Central Asia, Afghanistan and the Gulf, with Iran's "supreme guide" as the caliph.
Last August, Iranian President Mahmoud Ahmadinejad presented a broader version of that strategy to the Islamic Majlis (parliament) as his government's action plan. In it he said the Islamic republic had to prepare for a clash of civilisations between Islam under Iranian leadership and the West led by the US.
Ahmadinejad has asserted that the Islamic republic intends to resist "George W. Bush's plans for an American-style Middle East", and would fight to impose its Khomeinist model. He has dismissed the Arab states of the Gulf as "petrol stations, not real countries" and called for an "Islamic revolution" in Egypt and North Africa.
Tehran is also using the Hezbollah, which it founded and controls, to frustrate Lebanon's hopes of democratisation.
And last month, in a trip to Damascus, Ahmadinejad offered a broader interpretation of the Iran-Syria Defence Cooperation Agreement of 2002 to commit Tehran to supporting President Bashar Al Assad's beleaguered regime against its "internal and external enemies". According to Damascus sources, he asked Assad to "stand firm until Bush and the Americans leave the Middle East".
The immediate effect of Ahmadinejad's visit was a hardening of the Syrian position vis-à-vis the UN's investigation of the murder of former Lebanese prime minister Rafik Hariri.
One thing is certain: the Khomeinist regime is determined to reshape the region and, if possible, the world after its own fashion and will use whatever it takes, including a nuclear arsenal, to pursue its design. For those who, for whatever reason, do not like that design the only option is regime change in Tehran.
Which brings us to the third question: does anyone have the stomach for such an enterprise? Well, that is the question.
Iranian author Amir Taheri is a member of Benador Associates.