It is a question that has been asked repeatedly since the 1979 revolution, and one for which there are few ready answers. Commentators gloss over the tensions between the supreme leader, the president and the parliament -- let alone the power invested in the clerical establishment, the Revolutionary Guard and the bonyads (or foundations) that make up the Iranian state.
Yet it is exactly these relationships that determine the course of Iranian politics, from its nuclear ambitions to the chances of democratic reform. In step with this week's Iran issue, we introduce you to the power relationships that lie beneath the political picture, and the events that put them in place.
The supreme leader
Khamenei (left) gives a speech next to the newly appointed judiciary chief, Sadegh Ardeshir Larijani, during a meeting in Tehran in August 2009. Photograph: STR/AFP/Getty Images
The highest authority in the Iranian constitution, this dual political and religious role was made to fit Ayatollah Ali Khamenei's predecessor, Ruhollah Khomeini, in the aftermath of the revolution. It is based on Khomeini's doctrine of the velayat-e faqih, or the "guardianship of the jurisconsult"; the idea that the community should be guided by a religious jurist, in expectation of the coming of the Hidden Imam.
The supreme leader should be the highest spiritual authority within Shia Islam, a marja-e taqlid ("a source of emulation") or a grand ayatollah. The 1989 succession of Ali Khamenei to the role marked a shift in the Islamic Republic from religious attitudes to authority to political expediency, as Khamenei was only a hojatoleslam, or "proof of Islam" -- a lower clerical rank.
The supreme leader has power over the army, the revolutionary guard, the Basij militia and the judiciary, primarily through appointing the leaders of each group. It was this "mini-state" that his predecessor created in the aftermath of the 1979 revolution that allowed Khamenei to establish clerical supremacy. The supreme leader's power is almost without limit: Khamenei had the final word on last year's disputed presidential election.
The current Iranian president, Mahmoud Ahmadinejad, gestures while waiting for the arrival of Oman's leader, Qaboos Bin Said, at the presidential offices in Tehran on August 4, 2009. The sultan of Oman became the first foreign leader to visit Iran since Iran's controversial presidential vote last year. Photograph: BEHROUZ MEHRI/AFP/Getty Images
The most powerful political post in Iran that can be called democratic, the president of the Islamic Republic is elected from a list that is vetted by the Guardian Council. The president serves a four-year term for a maximum of two terms.
The power of the president is limited in the constitution, and is dwarfed by the influence of the supreme leader, the Guardian Council and other groups that make up the political centre. The presidency of Mohammad Khatami in 1997-2005 exposed these limitations; a reformer who offered a détente with the west, his foreign policy positions could never be anything more than symbolic, and his domestic reforms were obstructed by unelected loyalists to the regime.
Notionally, the president is the functional head of the executive. The president appoints the cabinet, subject to parliamentary approval, and is an international figurehead. In practice, however, power over defence and major foreign policy decisions falls under the authority of the supreme leader.
The Majlis: the Iranian parliament
Iranian students attend a parliament session in Tehran in November 2009. Photograph: ATTA KENARE/AFP/Getty Images
The Majlis represents the second democratic arm of the Iranian constitution, alongside the presidency. Its 290 members serve four-year terms. The Majlis has the constitutional power to vet and impeach cabinet ministers (and even the president), and introduces and passes legislation.
The major barrier to the power of the Majlis is the Guardian Council, which regularly bars candidates from standing, and vetoes parliamentary legislation. This constitutional deadlock has long been a feature of the politics of the Islamic Republic, and led to the creation of the Expediency Council in 1988.
The speaker of the Majlis, currently Ali Larijani, is an important spokesperson on domestic and international affairs. Even before the 1979 revolution, the Majlis was an important home of Iranian nationalism. Its roots are grounded in the constitutional revolution that took place between 1905 and 1911. Its importance should not be overlooked.
The head of the Iranian Guardian Council, Ahmad Janati, delivers the Friday prayers sermon at Tehran University in October 2009. Janati warned against an anti-government demonstration to counter an official commemoration of the storming of the US embassy. Photograph: BEHROUZ MEHRI/AFP/Getty Images
Iran's executive is made up of councils with varying, low levels of accountability. The most important is the Guardian Council. This body is made up of six clerics appointed by the supreme leader and six jurists nominated by the parliament from a list prepared by the judiciary -- whose head, of course, is appointed by the supreme leader.
This body has the power to veto parliamentary legislation, shut newspapers and bar presidential and parliamentary candidates. Depending on your perspective, it is either the protector of revolutionary values or the scourge of political reform in Iran.
The two other important bodies are the Expediency Council and the Assembly of Experts, both headed by Ayatollah Rafsanjani, a key power broker in the Islamic Republic.
The supreme leader appoints the Expediency Council, a body created to resolve constitutional deadlock between the Majlis and the Guardian Council. In practice, its membership ensures a heavy bias towards the establishment. The Assembly of Experts is made up of clerics elected from a list vetted by the Guardian Council, and its nominal role is to appoint and monitor the supreme leader.
Iranians hold portraits of Iranian cleric Grand Ayatollah Hossein Ali Montazeri during his funeral procession in the holy city of Qom on 21 December 2009. Photograph: AFP/Getty Images
A short drive south-west from Tehran, Qom centres on the shrine of Fatima, the sister of Imam Reza, on the bank of the Qom river. The clerical centre of Shia Islam, it is also an immensely important political base, due to its proximity to the capital and the overlap between the spiritual and political authorities.
Housing tens of thousands of seminarians, the city has expanded since the revolution. Large sums of money -- in the form of Islamic taxes and alms sent by followers -- come to the marja-e taqlid ("sources of emulation") who reside there. Normally seen as a conservative body, the marja are among the few with any authority to criticise the supreme leader. Some have questioned Khamenei's right to be considered a marja.
The recently deceased Ayatollah Montazeri was a prime example of the power of Qom, and his death was seen as a rallying point for reformists. Once nominated as a successor to Khomeini, he was cast out of the political centre for criticising the supreme leader, and remained a vocal critic of the government until his death.
The Revolutionary Guard
Iranians carry the coffin of General Nur-Ali Shushtari, the deputy commander of the Revolutionary Guard's ground forces, killed near the Pakistani border, during a funeral in Tehran outside the Revolutionary Guard garrison on 20 October 2009. Photograph: BEHROUZ MEHRI/AFP/Getty Images
A military force and corporation estimated to be worth billions of dollars, the Revolutionary Guard is the latest pressure point for those wishing to exert pressure on the Iranian state.
The Revolutionary Guard stands in command of the Basij, a paramilitary organisation that was established by the dictat of Ayatollah Khomeini. Its foot soldiers are known as "Basijis", a morality police that monitors the public for correct Islamic dress, makes sure that young, unrelated and unmarried Iranians are not walking or driving together in the streets, and so on.
After the hostage crisis of 1979-1981, the Revolutionary Guard moved into the US Embassy in the centre of Tehran, which was renamed "Den of Spies", and used it as a training base. It expanded to a full fighting force in the Iran-Iraq war. It was the Revolutionary Guard that captured the British sailors in the Persian Gulf in 2007.
The Revolutionary Guard is intimately associated with Iran's foundations, and is suspected of links to Hezbollah in Lebanon. The US Secretary of State Hilary Clinton has said that the force is "supplanting the government" and creating a "military dictatorship".
Hossein Shariatmadari, the director of the hardline Kayhan newspaper group, owned by Iran's largest foundation, sits next issues of the newspaper at his office in Tehran, 16 September 2007. Photograph: BEHROUZ MEHRI/AFP/Getty Images
When Muhammad Reza Shah Pahlavi was driven from Iran by the 1979 revolution, he left behind a huge swathe of assets. The Pahlavi foundation was renamed the Foundation for the Oppressed, a charity entrusted to helping veterans of the Iran-Iraq war. Thought to be worth as much as $12bn, this foundation controls large amounts of Iran's economy. Along with numerous companies, factories and mines, the foundation owns the Kayhan and Ettela'at newspapers.
The Foundation for the Oppressed is just one of several bonyads intimately related to the Revolutionary Guard and the political centre around the supreme leader. In the context of Iranian politics, the foundations represent the vested interests of the unaccountable and the spoils of the 1979 revolution. They have thus far proved beyond the reach of the democratic arms of the state. Any attempt to pull the Iranian state away from clerical hegemony comes up against the bonyads.
This piece accompanies Henry Smith's article, "Iran: the people"