Yet again, we hear the cry of the old economic religion: repent before it is too late; the wages of fiscal sin is death. But is it already time to retrench? I doubt it. At least, we must recognise the risks: delayed retrenchment poses the danger of inflation and even default; premature retrenchment threatens recession and even deflation, as I argued last week. Having barely survived the biggest financial meltdown in history, we need to appreciate that these downside risks are serious.

Some argue that the economy is always in equilibrium – that, in the words of Voltaire’s Dr Pangloss, everything is for the best in the best of all possible worlds. Others argue, with Andrew Mellon, US secretary of the Treasury under Herbert Hoover, that, after a big credit boom, we should “liquidate labour, liquidate stocks, liquidate farmers, liquidate real estate …it will purge the rottenness out of the system.”

I am not addressing inhabitants of either of these caves. I am addressing those who recognise that past mistakes have put the world economy into a deep hole and want to escape as quickly as possible. Yet sensible people believe that the biggest danger now is delaying fiscal tightening. They do so for four reasons. First, they fear that the financial markets, having turned on Greece, Portugal and Spain, will soon turn on the UK and even the US; second, they believe that deficits crowd out the private spending needed for recovery; third, they argue that high deficits must lead to inflation; and, finally, they believe fiscal deficits fail to support demand.

Let us look at where we now are, courtesy of the financial balance approach of the late Wynne Godley. This forces us to examine how the private sector is behaving. In 2010, according to the International Monetary Fund’s latest forecasts, the private sectors of every large high-income country will run a huge excess of income over spending. This is forecast at 7.8 per cent of gross domestic product for these countries as a group, at 12.6 per cent for Japan, at 9.7 per cent for the UK, at 7.7 per cent for the US and at 6.8 per cent for the eurozone.

What we are seeing, in short, is an epidemic of private sector frugality – just as many economic doctors recommended. Yet such thrift entails either current account surpluses or fiscal deficits. Of these countries, only Germany and Japan have current account surpluses. The rest are capital importers. These countries will duly run fiscal deficits that are bigger than their private surpluses. We have, as the hysterics note, a tide of fiscal red ink.

Which came first – private retrenchment or fiscal deficits? The answer is: the former. In the case of the US, the huge shift in the private balance between the fourth quarter of 2007 and the second quarter of 2009, from a deficit of 2.2 per cent of GDP to a surplus of 6.6 per cent, coincided with the financial crisis. The fact that aggregate demand and long-term interest rates tumbled at the same time shows that the collapse in private spending “crowded in” the fiscal deficits. Wild private behaviour drove the wild public behaviour.

In his recent FT column, Jeffrey Sachs of Columbia University argued that fiscal stimulus was unnecessary: monetary policy would have been enough. I disagree. Despite the most aggressive monetary policy ever, private sectors moved into huge surpluses. Monetary policy was “pushing on a string”. The fiscal offsets – overwhelmingly due to built-in fiscal stabilisers, not the discretionary stimulus – helped sustain demand in the crisis. But they were insufficient, even with monetary support, to prevent deep recessions. The argument that stimulus was unnecessary is hard to accept. It is easier to believe it was too small, albeit also ill-targeted.

So how quickly should deficits be eliminated? We must recognise the danger here: cutting public spending will not automatically raise private spending. The attempted reduction in the structural deficit might lead, instead, to a rise in cyclical fiscal deficits, which would be running to stand still, or to a reduction in the private surpluses only because income fell even faster than spending. Either outcome would be grim. Yet neither can be ruled out.

As long as output remains depressed, the fiscal support is most unlikely to be inflationary. Nor will it crowd out the private sector: it is more likely to crowd it in. The big question, then, is whether deficits can be financed. My answer is: yes. Remember that so long as the private sector runs financial surpluses it must buy claims on the public sector, unless the developed world as a whole is about to move into huge external surpluses.

True, the private sector can pick and choose among governments. But it is unlikely to abandon the US, at least. It has shown no sign of doing so, so far. The problem for peripheral Europeans is that they have little chance of an early return to growth. Markets do not trust in the political sustainability of hair-shirt economics. It is not so much fiscal deficits as an inability to grow out of them that is worrying.

The best policy is to put together measures that sustain strong growth in demand in the short run, while constraining the huge deficits in the long run. This is walking and chewing gum at the same time. Why should that be so hard?

Yet it would now be particularly damaging for fiscal austerity to overcome the European economy and so force beggar-my-neighbour outcomes on the hapless US. As Fred Bergsten of the Peterson Institute for International Economics in Washington noted in the FT last week, such policies could be very dangerous. Thus, far from being stabilising, premature fiscal retrenchment threatens destabilisation of the world economy. In this case, a decision to turn the eurozone into a huge Germany would – and should – be seen as an act of mercantilist warfare upon the US. How long would the latter put up with the hypocrisy of surplus countries that blame borrowers for the deficits their own surpluses make inevitable? Not much longer, would be my guess, at least now that the US government has become the world’s borrower of last resort.

Yes, I understand that huge fiscal deficits make people nervous. I understand, too, the desire to make solvency credible. But following fiscal rules blindly, while ignoring what is going on in the private sector or in external balances, is a recipe for disappointment and political conflict. Fiscal stabilisation that supports growth is welcome. Premature fiscal stabilisation that undermines it is yet another folly.

martin.wolf@ft.com

More columns at www.ft.com/martinwolf

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