The biggest debate in politics is also a game of “what-if” which neither side can conclusively win.
As we know all too well, the economy is not recovering as quickly as expected.
The growth rate is lower than predicted, which means tax revenues are also lower while benefit payments are higher.
George Osborne, the Chancellor, argues there are a number of reasons for this, none of which can be pinned on him.
The turmoil in the eurozone has affected the UK – not as much as it will if the euro actually collapses, mind – while it has emerged that Labour made an even bigger mess of the economy than anyone realised, he argues.
Rising oil prices, caused partly by revolutions and general chaos in the Middle East, is another factor.
But Ed Balls, Labour’s Shadow Chancellor, has another analysis.
He reckons that slow economic growth is a result of the Chancellor’s attempts to reduce the deficit by cutting spending.
Paradoxically, according to Mr Balls, by cutting spending the Government actually ends up spending more, and borrowing more, because it has to pay more in unemployment benefit and receives less in taxes.
If Ministers had followed the Balls strategy of keeping up spending and pumping more money into the economy to build hundreds of new homes then we’d all be better off today. That money would have created or saved jobs, he claims.
It seems to me that the difficulty facing Mr Balls is that his basic argument – that the Government should increase spending in order to keep borrowing down – seems counter-intuitive (as the only way Mr Osborne could spend more in the immediate term is to borrow more).
That doesn’t mean it’s wrong, as John Maynard Keynes might have said.
Keyensian economics, including the idea that Governments can stimulate the economy during a downturn by investing in infrastructure, has come back into fashion since the banking crisis began.
And if you’re going to pay someone to sit on the dole, it could be argued that you may as well use that money to create a job for them – even if, as Keynes once suggested, it involves burying bottles of money for someone else to dig up again.