The financial markets got the message - thus giving the Reserve the self-generated justification that it had to act because the market was expecting it to - but most business economists didn't. In their naivety, most economists regard the word of the governor as more reliable than media speculation. Despite the rate cut - and the assumption of at least one further cut - on Friday the Reserve shaved its forecast for real growth this year by 0.25 percentage points to 2.75 per cent, but left its forecast for next year unchanged at a midpoint of 3.5 per cent. So what was so worrying that the Reserve, having sat on its hands for 18 months, couldn't wait another four weeks to protect its reputation? The old story. This year has long been expected to be when mining investment spending falls hardest, leaving a huge hole in activity, to be filled by the resurgence of the non-mining economy, particularly ordinary business investment. The Reserve worries that business investment isn't recovering fast enough. So, despite having already cut the official interest rate from its peak of 4.75 per cent in late 2011, it decided to take off another click or two.

It might make all the difference, but I doubt the high cost of borrowing is what's holding businesses back from expanding. More likely, they don't see any great scope for making a bigger buck, and they're not in any mood to try their luck. As central banks in other developed economies have discovered, when "animal spirits" aren't helping, you can get to a point where even exceptionally low rates do little to encourage borrowing and spending, when cutting rates to encourage growth is like "pushing on a string". There's one exception, however: borrowing for homes. The main reason the Reserve has waited so long to cut rates further is its fear this would do more to encourage musical chairs in the housing market - the buying and selling of existing homes - including yet more negative gearing. This doesn't do much to increase economic activity, but does bid up house prices and so add to the risk of a price bubble developing, particularly in Sydney and Melbourne. It also leads to faster growth in household debt. Saul Eslake, of Bank of America Merrill Lynch, notes that after stabilising for some years, the ratio of household debt to annual household income has been rising to more than 150 per cent and will now go higher.

With their official interest rates down virtually to zero, the Americans, Europeans and Japanese have already got close to the limits of monetary policy. They've had to resort to "quantitative easing" (creating money out of thin air), but this has done a lot more to distort exchange rates and inflate prices in asset markets than it has to encourage real economic activity. At 2.25 per cent, our official rate is still well above zero but, even so, we're close to the point where the costs and risks of a rate cut threaten to exceed the benefits. The upshot of the great battle between Keynesians and monetarists in the 1970s was agreement that monetary policy was the most effective way to fight the opposing evils of inflation and unemployment. By the 1990s, some concluded that manipulation of interest rates by independent central banks had conquered the problem of keeping economies on an even keel. Yeah, sure. We discovered a fatal weakness in the new macro management: monetary policy was great at controlling ordinary inflation, but when used to stimulate weak demand it was prone to encouraging excessive borrowing and asset-price bubbles which, when inevitably they burst, caused deep and protracted "balance-sheet" recessions.