A weariness besets the world. America drifts, Europe crumbles, China slows, markets everywhere are tired and broken. A sort of nervous exhaustion stalks societies, our problems feel bigger than our solutions.

This stagnation is a symptom, the disease is the lack of hope. The cause is intellectual fatigue; the world is dying for the want of a new idea. But this inertia won't last forever. Sooner or later the human spirit will rise and change will come.

Most of human history is drudgery, things are the way they are because they've always been the way they are. The slave, the peasant, the serf, the toiler, the tenant farmer and disposable cubicle drone all submitted to their miserable fate quietly, generation after generation.

We look at the past and wonder how they put up with it. The answer is that they didn't see the possibility of a better way. And their betters made sure they never would.

The ruling class of any and every time uses the same strategy to stay on top. The words change, but the song remains the same: "There is nothing you can do. It's God's will. It's the market's will. Politics and government are useless, they only make things worse."

Fatalism is a philosophy, but more than that, it's a strategy, it's a weapon. Nothing will keep the people quieter, more passive, more bovine, than carefully nurtured cynicism. Discredit the idea of political change and you can rule behind the walls of your castle or your gated community for a thousand years.

Politics is possibility. Politics is ideas, and ideas are dangerous. The survival of any existing power structure is dependent upon the elimination of possibility. In troubled times the ruling classes strive to kill that possibility before it can be born. Their position depends on it.

We live in such a time.

Politics is a dirty word at the moment. That is not an accident. Discredit politics and you neuter democracy. Democracy is the only check on the unlimited powers of brute force and money. Politics is the only way the powerless can join hands and make change.

There is little mystery about what needs to change. Economic inequalities have grown grotesque, environmental exploitation rages unchecked, markets are so out of control even the rich are terrified. But nothing can change, nothing deep and fundamental, until the status quo is confronted by a new idea. Cynicism and despair never change the world, no matter how dark times get.

But let a new idea come into the world, let some Voltaire or Marx or Payne or Keynes write a pamphlet, giving the people a plausible path they can believe in, and watch out. Show them a way and they'll take that way, if they have to tear down the barricades with their bare hands.

The path can be right or wrong, short or long, peaceful or violent. It can lead to Philadelphia or Pol Pot. Where that path takes you is unpredictable. But the triggers of change are highly predictable, they're mathematical.

Revolution happens when the people's political ideas overpower their socioeconomic submissiveness. Then change is inevitable.

Random events happen every day, but some days aren't random. They give us the Magna Carta, the American Revolution, the French Revolution, the fall of the Berlin wall, the Arab Spring.

The pressures that led to the burning of the Bastille built over centuries; they burst in a month. The Berlin wall was reviled for thirty years; it fell in a weekend. What made the people revolt after years of submission? Why did they take so long?

Because before then, the people's political expectations were lower than their economic expectations. They didn't see their power, they couldn't imagine a way forward.

And then a street vendor in Tunisia sets himself on fire. It strikes a chord in the people, they gather in forbidden numbers. The penny ante dictators in one fragile society lose their nerve and flee. An example has been set, a new possibility emerges into the public consciousness. Nothing has really changed except where before there was only a blank wall of fatalism and resignation, now there is a road, a possible path to a better future. People see that road and they take it.

That is the revolution equation. When the sum of the people's political expectations exceeds their economic expectations, they are ripe for revolt. It takes only a spark, a Facebook post or a timely tweet. It only takes an idea.

Got one?