Will it bear fruit or be a bitter harvest?

Right now, this is the most important question in geo-politics.

It is not in truth a stark binary choice, of course. The Arab revolutions might be a little bit of both and a lot of something else as well. But this is the key question: who owns the future, the liberals or the Islamists? In trying to work out an answer perhaps three dimensions of experience can help us grope towards a guess: the history of revolutions; the nature of Arab societies; and the behaviour of the actors in the present dramas across North Africa and the Arabian peninsula.

The history of revolutions would make you fairly pessimistic. But why should Arab revolutions resemble others? The answer is because human nature is essentially one and revolutions are a category of human experience that seems to have recognisable dynamics.

In the 19th century when people spoke of revolution they had the French revolution in mind. It certainly started with a democratic instinct and a revulsion against absolute power, but soon degenerated into mob rule, blood lust, totalitarian ambition and ended in the restoration of tyranny.

The American revolution ended much better, but it was less a social revolution and more a simple war of national independence.

For most of the 20th century, revolution meant the Bolshevik revolution in Russia in 1917. Who could oppose the overthrow of the tsar? For a time, the moderate and sensible Kerensky ruled in Moscow with Russia racked by World War I. But Lenin had the insight that state power was everything and the ruthlessness to seize it.

After that, communist consolidation was not so difficult, though extremely bloody.

Are today's Islamists effective Leninists, as Hamas is in the Gaza Strip and the mullahs are in Iran?

More recently there are two new models of revolution: the 1979 overthrow of the shah in Iran; and the colour revolutions in Eastern Europe, the orange revolution in Ukraine and the rose revolution in Georgia. They followed in the footsteps of the velvet revolution in Czechoslovakia.

The European revolutions were unambiguously liberal. Their progenitors wanted what their West European neighbours had. They emerged from societies with their own histories of liberalism and sometimes democracy.

The Iranian revolution was unambiguously an Islamist revolution. Genuinely liberal forces combined with the Islamists against the greater evil of the shah, only to find eventually that the Islamists themselves were the greater evil.

Other revolutions have suffered similar fates. Who could argue that it was wrong to get rid of Batista in Cuba, or Somoza in Nicaragua, or even Chiang-Kai Shek in China? Yet in each case a vastly more brutal rule replaced the deposed dictators.

One thing the East Europeans had going for them was proximity to Western Europe. Generally the dynamics of the Middle East have been poisonous. But in recent years North Africa has grown much closer to Europe, not least through immigration.

I was in Casablanca a few weeks ago and it looked like any Mediterranean city. It may be that the internet has also lessened the importance of geographic regionalism and perhaps enhanced a different kind of regionalism, the regionalism of youth and common interests.

Nor should we ignore another element of regionalism. There is now an Arab democracy, Iraq. With all its difficulties, it introduces the idea of freedom of expression into the Muslim Arab world.

Overall, the nature of Arab societies does not give you much cause for optimism, though. The internet and all its offshoots spread both liberalism and illiberal poison. The mass media in Arab societies propagate the worst of cultural and religious hatreds. In Indonesia last week a shrewd intellectual told me that his society was terribly fortunate it had modernised before it democratised.

Yet although the intolerant and hate-filled Islamist ideologies remain strong in the Arab world, it is certainly possible to detect a weariness with them too.

Bernard Lewis, the great scholar of Islam, prefigured this in a superb book, What Went Wrong?, published a decade ago.

"For many centuries," Lewis wrote, "the world of Islam was in the forefront of human civilisation and achievement." Then over centuries it fell apart and became a slum. Lewis's book is an investigation into why this happened.

But Lewis seemed to predict the Arab spring we are now witnessing. He wrote: "The blame game continues, and shows little sign of abating. For the governments, at once oppressive and ineffectual, that rule much of the Middle East, this game serves a useful, indeed an essential purpose: to explain the poverty that they have failed to alleviate and to justify the tyranny they have intensified . . . But for growing numbers of Middle Easterners it is giving way to a more self-critical approach. The question 'Who did this to us?' has led only to neurotic fantasies and conspiracy theories. The other question - 'What did we do wrong?' - has led naturally to a second question: 'How do we put it right?' In that question lies the best hope for the future."

At its essence I suppose this question is whether Arab societies have modernised to the extent that they want, and can sustain, modern political systems, which means democracy of one kind or another.

And finally, perhaps the greatest cause for optimism is the demeanour of the demonstrators themselves. There have been extremists, anti-Semites, wild anti-Americans, among the demonstrators but they have been in the minority. Mostly the demonstrators have conducted themselves with modesty and restraint, and their demands have been explicitly democratic.

The involvement of internet technology and the involvement of youth are exciting but on their own they don't determine the values of a revolution. Nazism and communism were both once highly popular with young people and gloried in their exploitation of new technologies. Rather, the moderate personal behaviour of many of the demonstrators is the genuine sign of hope.

I have been having a friendly dialogue with Jon Faine on Melbourne ABC radio on all this these last few weeks and he is inclined to think I'm unduly pessimistic. The truth is I am absolutely certain that I do not know how the Arab revolution will turn out. Most revolutions disappoint, some very bitterly. I hope this is the exception.