How is it that history makes an unexpected leap forward?
Take the sudden onset of the economic crisis. We were told this could never happen again, but banks are failing, the financial system is in turmoil and a recession is opening up beneath our feet.
The recession is hardly the only example in recent years of a sharp disruption to the flow of events. The 9/11 attacks and their consequences were utterly unforeseen, and marked a turning point after which many important things in the world were never the same again.
Back in 1989 the fall of the Berlin Wall was another history-altering event that seemingly came from nowhere in a society that appeared unchanged year after year. Such events do not, by definition, happen every day. But they happen sufficiently often for us to feel the need to explain them.
Explaining change is what the Marxist method of analysing society is all about. History shows us that certain types of change, like these sudden transformations, often recur, and Marxists have developed tools that help us recognise and explain them.
One of these tools is called the dialectical method. The origins of this term lie in Greek philosophy where "dialogue" - the clashing of two or more opposed points of view - was seen as the way to get at the truth. It is this process of discussion and debate, rather than any single point of view, which is supposed to represent the truth.
If instead of just looking at ideas as developing through the contradictions between different positions in a debate we also look at social institutions - like the economy or the state - as developing through a process of contradiction, we can begin to see how this method can describe social change.
But what does this mean? Everyone can see that in a debate there is a contradiction and maybe the truth emerges from this clash of ideas. But what does it mean to say that the economy or the state develops because of contradiction?
It means we are saying that these institutions are not stable, monolithic things. Rather they are prone to change because they contain contradictory impulses.
The market, for instance, constantly drives to expand because it is based on competition. Each firm is out to maximise production and market share, and to drive down costs. But the effect of each firm blindly pursuing these goals is that periodically too much is produced, firms then cut back because they have unsold goods, they lay off workers and a recession begins.
Capitalism, Karl Marx pointed out, rests on the contradiction between the collective production necessary to make the system function and the privatised accumulation of profit inevitable when a tiny elite own the factories, offices, banks and so on.
Quite simply, there is a contradiction between the drive to accumulate and the blind competitive nature of the market. Both are indispensable to capitalism, but they cannot coexist in a stable form.
The state embodies its own contradictions. It is meant to represent everyone in society - but in reality it represents the interests of the economically dominant class. Moreover, states compete with one another economically and militarily. So despite statesmanlike professions of peace and cooperation by world leaders, domestic instability and war, or the threat of war, are built into the state system.
So why do these contradictions suddenly explode, perhaps after years of quiet development?
In institutions based on contradictions it is quite usual for change to occur gradually for long periods and then erupt in a sudden "catastrophic" moment.
Indeed this is a feature of many different sorts of change, even in the natural world. Water that rises in temperature by one degree at a time shows no dramatic change until it reaches boiling point when it "suddenly" becomes steam. At that point its whole nature is transformed from being a liquid into a vapour.
Lower the temperature of water by a single degree at a time and again there is no dramatic change until it reaches freezing point, when it is transformed from a liquid into a solid - ice.
Dialecticians call this process the transformation of quantity into quality. Slow, gradual changes that do not add up to a transformation in the nature of a thing suddenly reach a tipping point when the whole nature of the thing is transformed into something new.
We can see the sudden eruption of the economic crisis in this way. The gradual process of extending the subprime mortgages in the US, the deregulation of the banking industry and the long attack on working class living standards suddenly reached a critical point and tipped the whole system into a global crisis.
Similarly, a long gradual process stood behind the events of 9/11: the support of the US for Osama Bin Laden and the Taliban in the Afghan war with Russia in the 1980s; US support for the corrupt regime in Bin Laden's home country, Saudi Arabia; the US bases set up in Saudi Arabia during the first Gulf War in the early 1990s; the new imperial drive of the US after 1989 and its hostility to the Taliban. Much of this went unremarked upon until the tipping point of 9/11 was reached and a qualitatively new situation became self-evident.
Such sudden transformations can also happen in the class struggle. Grievances that have been tolerated for years can suddenly explode in anger. The latest insult can be, as the old dialectical phrase has it, the straw that breaks the camel's back.
In a way every strike, every new protest movement and, certainly, every revolution emerges in this way. And this is what our rulers fear - that we will understand the fragility of their system and the ability of our class to suddenly react to its crises.
This is why Marx described the dialectic as "an abomination to the bourgeoisie" and why Lenin said of this method that it "alone furnishes the key to 'self-movement' of everything existing; it alone furnishes the key to 'leaps', to the 'break in continuity'...to the destruction of the old and the emergence of the new".
The Algebra of Revolution by John Rees; Postface to the Second edition of Capital by Karl Marx