Egypt unrest: Possible scenarios
For Egyptians, and the millions of Arabs watching closely across the Middle East, these are hugely exciting times. But for all the hope for change, there are also enormous dangers. These are three broad scenarios that could result from the events in Egypt.
CUT AND RUN: MUBARAK GIVES UP PRESIDENCY
The protesters coming out on to the streets of Egypt's cities clearly want Hosni Mubarak, who has been in power for 30 years, to give up the presidency immediately. The most common demand, shouted and painted on banners, is the Arabic word "irhal", meaning simply "go".
In his speech on Friday night, Mr Mubarak offered concessions, but gave no indication that he understood the anger of the protesters. For them, he is the problem, not his government or the fact that the country had, until he appointed Omar Suleiman, lacked a vice-president. Mr Suleiman, a Mubarak stalwart, now appears to be in the position of designated successor.
In this scenario, the army would be the key institution that indicates to the president that he must leave because he is the main cause of instability. It would then take charge of securing the country.
But for some Egyptians, and certainly for Western governments and Israel, the sudden disappearance of Mr Mubarak represents potential disaster. The fear is that a power vacuum would result in the sort of chaos in which armed Islamist groups might thrive and the army would need to take over the running of the state.
So far, Mr Mubarak has given every indication that he is resisting all pressure to go.
STICK TO HIS GUNS: MILITARY AND POLICE CRUSH PROTESTS
Though the army and police have been on the streets in great numbers, and many people have died in clashes, the state has not fully unleashed its security forces on the protesters.
Normally, the riot police are in charge of dealing with protests and they are usually highly efficient at mass arrests and breaking up crowds with controlled brutality. But the police may have been overwhelmed by the number of protesters, and their determination and fearlessness.
Mr Mubarak could try to ride out the protests, hoping the demonstrators will tire before he does. He could also issue the order to simply crush the demonstrations. For this, he needs the army.
The level of violence needed to drive the crowds from the streets would almost certainly leave many dead and could inflame the situation.
Washington, Mr Mubarak's key Western ally, has explicitly called for restraint and an end to violence against protesters.
It is also far from clear that the army would follow orders to fire on unarmed crowds. A statement by the army on Monday said it would not use force against the protesters.
The military sees itself as non-political and the nation's saviour. To align itself with the president and against the will of the people would be to lose its legitimacy and privileged position in Egyptian society.
A collapse in security would also do great damage to Egypt's economy, with tourists staying away and factories shutting for long periods. The price of oil has already risen sharply on fears that traffic through the Suez Canal being disrupted.
TRANSITION: PROMISE TO LEAVE, OPPOSITION JOINS GOVERNMENT
Under this scenario, chaos and violence are avoided, and Mr Mubarak bows out gradually. He might promise to stand down after presidential elections due for September this year.
This would allow parts of the ruling system to survive, but not the president and his closest associates. This is probably what Washington means by an "orderly transition".
In this scenario, Mohamed ElBaradei could emerge as a compromise figure to oversee the transition and establish new rules for elections, for president and parliament, that Egyptians can believe in.
In any free and fair election, the Muslim Brotherhood would be expected to win a large part of the vote. It is well-supported and respected within Egypt, largely for the work of its charities. But it is untested in government and poorly understood - especially in the West.
How would it reconcile its aim of creating a state ruled by Islamic law with its stated support for democratic principles? Are these mutually exclusive?
Can an overtly Islamist and conservative organisation govern a society which includes about 10 million Christians?
How would it, in government, manage Egypt's relations with the US and Israel?
The Muslim Brotherhood are certainly not the Taliban, but are they close enough to, say, Turkey's AK Party - a moderate Islamist grouping - to come to some kind of workable relationship with the military and the West?