Karl Marx and Friedrich Engels suggested two reasons why revolution is necessary.
First, there is no other way that the ruling class will give up their power, property and privilege.
On that, all kinds of revolutionaries agree – both those who think minorities can change the world, and those who look to the revolutionary activity of the majority.
The second reason is distinctive to Marxism. It is that only in revolution can the working class 'succeed in ridding itself of all the muck of ages and become fitted to found society anew', as Marx himself put it.
That's a view of revolution as the act of great mass movements. It's tied to a view of socialism as a vast extension of popular democratic control over all aspects of society.
It also identifies a key obstacle to socialism – the 'muck of ages', those features of everyday life that impede the working class majority from being able to rule.
A working class that today is alienated, divided, and powerless cannot wake tomorrow fully equipped to run the world democratically.
It has to change itself through struggle. The key bridge is participation in mass movements of revolt. Only such movements contain the possibility of becoming movements aiming at workers' power.
Already, early in this new century, mass strikes are reviving across the world. They, along with other kinds of mass revolts like that erupting in Burma, are not just important in their challenge to the rich and powerful.
They also initiate a vital process of collective self-organisation and introduce the beginnings of practical, mutual solidarity.
And not only that. The core idea tying us to the ruling class world of hierarchy and deference is the feeling that we amount to nothing. Class society is a system of organised humiliation.
In mass movements, people start to raise their heads. They begin to look their rulers in the eye, and notice how they blink and turn away. In mass movements, people laugh more and enjoy themselves.
In mass strikes and similar struggles, two other developments sometimes occur. Both point the way forward.
The first is when ordinary working people start taking over the running of bits of everyday life. This might seem mundane. Organising food supplies for a factory occupation or a long strike doesn't sound very revolutionary, but it's a vital material necessity, and it draws people into new forms of activity. Done badly, it hurts morale. Done well, it raises confidence.
The miners' wives in 1984-5 started with organising canteens, and went on to claim a central place in the strike committees.
In Seattle in 1919, the general strike committee commandeered lorries – issuing passes to drivers and controlling the movement of necessary supplies.
In Gdansk in Poland in 1980, the strike committee took over taxis and trams too. They put their own guards on the shipyard gates, checking who went in and out of the occupation. They also took over the loudspeaker system, using it to relay their talks with the government to the whole workforce.
In these and many other ways, mass movements enable people to start envisioning a new form of society, by starting to experience pieces of life under their own collective control. The beginnings may be small, but their potential is huge.
Often different struggles within capitalist society seem separate from each other, even antagonistic. Workers are divided by nationality, ethnicity, religion and gender. Sometimes in mass movements, different struggles fuse together.
The movement's new unity breaks down old divisions. Indeed, finding that unity is often a condition of success.
In the US, before black and white workers learned to organise together, they fought each other. One great achievement of the US strikes of the 1930s was the forging of black and white unity in the auto and steel plants.
Mass movements can thus challenge not just competition between individual workers but division into competing groups. Inherited forms of oppression can be rapidly undermined.
These are possibilities. They don't always occur, and they don't always realise their full potential. We'll look more at this next week.
Colin Barker is the author of Festival of the Oppressed: a history of Solidarnosc in Poland. It is available for £3 from Bookmarks – go to » www.bookmarks.uk.com