ADAM Smith is credited with first illustrating the law of unintended consequences. Smith argued in the field of economic theory that the individual, seeking only his own gain, was "led by an invisible hand to promote an end which was no part of his intention". He argued that "Nor is it always the worse for society that it was no part of his intention. By pursuing his own interest he frequently promotes that of the society more effectually than when he really intends to promote it"
In other words, each party pursuing solely its own advantage may unintentionally create a benefit for society as a whole. It is an argument which appears to hold true in the free market of election politics.
For having spent the campaign relentlessly and exclusively pursuing their own party advantage, both Gordon Brown and David Cameron are now forced to contemplate embracing a policy they fundamentally oppose – the introduction of proportional representation.
Be clear – delivering that reform in government would be the single biggest, most radical and most fundamental change to British politics arising from any election in recent decades. If it happens, it will be by far the biggest story of this campaign.
We have already seen Labour tip-toe towards the Liberal position with the pre-election offering of the Alternative Vote system. Post-election, they will have to go much further to stay in power. The Tories, frustrated by their inability to break free of the pack, are also being forced to make supportive noises. Michael Portillo, for one, believes Cameron will meet Lib Dem demands in order to form a government.
Neither party does so on any basis other than naked political ambition. But don't despise that, celebrate it. It is precisely because of those parties acting in their own self-interest – their desperate desire to become the government – that the greater good of a fair voting system is within reach.
In fact, if you trace it back, it is precisely the pursuit of that self-interest which got Labour and the Tories into this fix in the first place. The leaders' debates have utterly transformed this election. Those debates created the forum within which Nick Clegg has excelled and so advanced the Lib Dem agenda.
So why did Cameron agree to the debates? Essentially to seek advantage. He rushed into press in September 2009 to accept the invitation from Sky TV. He did so to look keen to engage with the public, to look fresh and bold. He wanted to contrast that apparent openness with the reluctance of a dour and outdated Labour Prime Minister. His statement of the time speaks of "the urgent need to reinvigorate our political system".
That much has been achieved. It is just that the party which has benefited is the Lib Dems and the reinvigoration might well involve transformation of the UK constitution and the ending of any future prospect of a Tory majority. Good job, Dave.
And Brown? Well he was really no better. Having hummed and hawed for a while, he ultimately had no choice but to participate or risk ridicule. Again, self-interest. But in agreeing to those debates, both Labour and the Tories planted the seeds of the Lib Dem transformation and made themselves the reluctant midwives of constitutional reform.
And here's a thought for Scotland– the arrival of PR would transform the fortunes of the SNP and break the Labour grip on Scottish representation at Westminster. That would be a greater success than anything the SNP has ever before achieved in a Westminster election. The SNP does not have to win this election ultimately to enjoy success.
In fairness, no-one saw this coming. But then, as I suppose Adam Smith would tell you, that's why they call it the invisible hand.
More widely, however, the debates themselves are starting to make me uneasy. Yes, they have captured the public's imagination and represent a shift in the dynamic of this campaign from party control to voter empowerment. The leaders are being forced out of their comfort zones and onto the hustings.
The problem is that three men, in three debates, in three English cities now represent the sum total of the modern British general election. The campaign is little more than coverage of the build-up to and aftermath of these showdowns. Is that over-reliance of political pantomime really what we wanted? Shouldn't we be troubled that public opinion is so utterly fickle, so over-impressed with image and with a few good debating points that the polls can swing so violently? Isn't that the danger of set-piece, winner-takes-all, trial by television?
Dianne Abbott last week expressed her concern that we were getting a US Presidential system without the checks and balances. That is an astute observation, because the impact of a victory in a UK general election is normally to deliver a working majority in the House of Commons which carries none of the counter-balance written into the American constitution. Moreover, the American campaign is so long that no stone is left unturned. Here, we are cramming these debates into a four week campaign with the obvious result that there is little oxygen for much else.
The culture and structure of our political system are different. Despite the efforts of Thatcher and Blair, Cabinet government and the maxim of primus inter pares still mean something. Instead, after the game-show theatrics of the debates, I almost expect to see Simon Cowell in the Speaker's Chair of the next Parliament. Now, if he commits to bringing Cheryl Cole in as the Parliamentary Macer…