Although many people have their doubts, the Reserve Bank cut interest rates last week believing it would help the economy grow faster and reduce unemployment. But how exactly is this meant to work?
Monetary economists believe interest rates affect the strength of demand (spending) in the economy via several "channels" or mechanisms. Eventually the effect on demand affects the degree of pressure for higher prices.
As we work through these channels we'll see why some people didn't want interest rates to be cut further, why some believe monetary policy (the manipulation of interest rates) is at a point where it's less effective and why others (such as me) believe the further cut risks fuelling a house-price bubble.
The first channel goes by the fancy name of the "inter-temporal substitution" effect. Inter-temporal means "between time periods" and it's making the point that the rate of interest is the opportunity cost of choosing to spend now rather than later.
If you want to buy a car but don't have the money to pay for it, the cost of buying it now rather than waiting until you've saved the money is the interest you pay on the loan. But even if you already have the money in the bank to buy the car, the opportunity cost of buying it now rather than later is the bank interest you forgo by taking your money out.
So when the Reserve brings about a fall in interest rates it's hoping the lower cost of borrowing (or the lower opportunity cost of reducing the money in your bank account) will encourage households and businesses to bring forward their spending on consumer durables and assets from a future period to the present period. This is inter-temporal substitution.
The next channel is the cash flow effect. In principle, cutting interest rates reduces monthly mortgage payments, leaving people with more cash to spend on other things. Equally, the lower repayments make it easier for would-be home buyers to go ahead.
Remember, however, that although almost all businesses have debts, only about a third of households have mortgages. Roughly a third have paid off their homes, leaving about a third renting.
This suggests that about two-thirds of households are "net lenders" (they have more money in bank accounts and the like than they owe on credit cards and personal loans), leaving only a third of households as "net borrowers".
But as any retiree will unhappily remind you, a fall in interest rates might be good news for borrowers, but it's bad news for lenders. So about two-thirds of households (including oldies and young people saving for a house deposit) will be left with less cash to spend on goods and services.
It's true, however, that the remaining third of households gain more overall than the two-thirds lose, because the amount they owe exceeds the amount the two-thirds have in bank accounts and securities.
This is why you'd expect the cash flow channel to be a further mechanism that, in net terms, was encouraging spending and growth. Trouble is, a high proportion of people with home loans leave their monthly mortgage payments unchanged despite the fall in rates. That is, they don't spend their saving in interest, they save it.
A third channel by which a cut in interest rates should hasten economic growth is the exchange rate effect. When our interest rates fall relative to other countries' rates - thus reducing our "interest rate differential" - this should make bringing foreign funds into Australia less attractive and so reduce the demand for Aussie dollars, causing it to fall relative to other currencies.
A lower dollar makes Australian businesses more price competitive by making our exports cheaper to foreigners and imports dearer to Australians. This should encourage greater Australian production of goods and services, increasing employment.
It's a nice, neat chain of logic but, as the Reserve notes in its description of the monetary channels on its website, they are "far from mechanical in their operation". Lots of other factors affect our exchange rate beside the interest differential.
There's a strong, but far from automatic, correlation between our dollar and the prices we get for our commodity exports. Our exchange rate is also affected by the things our trading partners do in their economies, such as manipulating their exchange rate by engaging in "quantitative easing".
Don't forget, our dollar was falling during the 18 months that our interest rates were unchanged.
Even so, my guess is that trying to keep the Aussie's recent downward momentum going was a big part of the Reserve's reason for cutting rates last week. It knows forex markets are affected by speculation and bandwagon effects that don't get much coverage in textbooks.
Another part of the channels story is that cutting the return on safe financial investments such as bank accounts has the effect of encouraging individuals and businesses to seek higher returns by buying riskier assets. Retirees move from bank term deposits to shares, while some households respond to lower interest rates by buying negatively geared investment properties.
Lower rates lead to more borrowing to buy houses, which pushes up house prices. Rising house prices encourage more people to buy, particularly investors seeking capital gain. If you're not careful this becomes a house price bubble that inevitably ends in tears.
Left out of the standard story about the channels through which lower interest rates cause faster growth is that the era of greater reliance on monetary policy has also been the era of credit-fuelled asset price booms and busts. As witness, the global financial crisis.
Why did the Reserve wait 18 months before cutting interest rates to a new low? Because it knows it's running a high risk of sparking a housing boom and bust. But with the economy now so weak, it felt it had no choice.