Central bankers are again hinting at a return to policy divergence but the past nine months have shown just how difficult it is to truly widen monetary policy settings without the anchor of an economy where rates are rising.
At the annual meeting of the world's top central bankers in Jackson Hole on the weekend, United States Federal Reserve chair Janet Yellen paved the way for a second interest rate rise in as many years in the world's biggest economy, saying that "the case for an increase in the federal funds rate has strengthened in recent months".
Since its historic December 2015 rate rise, Dr Yellen has failed to keep up with the pace of the Fed's interest rate rise forecasts, which still indicate two hikes to come this year. Japan introduced negative rates in January and the European Central Bank in March loosened policy even further, but neither has tested more accommodative ideas since then because of the growing consensus that their actions are no longer stimulatory but distortive.
The exception has been the Bank of England which turned to asset purchases and lowered rates to 0.25 per cent as part of its response to Brexit, in what was the BoE's first rate cut since 2009.
Angus Coote, executive director of Jamieson Coote Bonds, saw Dr Yellen's statement and similar commentary by vice chair Stanley Fischer as an attempt to jawbone interest rate expectations.
"If you look at Fed funds futures since 1994, when [former chair Alan] Greenspan hiked unexpectedly, the Fed has never hiked or cut interest rates without the probability of a rate hike being at least 60 to 70 per cent," he said.
On Friday, futures put the probability of a September hike at 32 per cent, that rose to 42 per cent after Jackson Hole.
"They're trying to jawbone the market, the market's saying 'we don't necessarily believe you'." December could be an appropriate time for the Fed to hike, Mr Coote said, if jobs momentum remains intact, and the election is decided. Markets see a 65 per cent chance of a December hike.
John O'Connell, chief investment officer for Macquarie Wealth Management, says scope for divergence has become a matter of degrees of "how far the policies can diverge before they start causing feedback loops on themselves" which as it turns out is much less than it was 30 years ago.
"We've seen an incredible amount of tariff reforms and supply chain reforms as well as opening up economies. We've got a far more integrated world today than we ever did before in terms of production of goods and services," he said. "Central banks are generally to some extent tied at the hip by their exchange rate policies around the world."
Assuming the US economy was booming, capital would leave the negative-yielding economies and flow to the US, raising the value of the US dollar which makes its goods and services more uncompetitive, he explained.
"I think they will raise rates this year, whether we get the first rate rise in September or in December is a moot point," Mr O'Connell said. "If the Fed was to raise to any degree, it takes the pressure off others [to ease further] which have got negative yielding rates.
"That's where we eventually need to get to, it's the normalisation of interest rates."
Mr O'Connell said that the next rate rise from the Fed could set up a correction in equity markets, perhaps as soon as the third-quarter earnings season for US companies. Were that to happen, he said, it would be wrong to blame the central bank because it has been signalling its intent to wind back what are supposed to be emergency level settings.
"The market is very expensive at the moment, the Fed has done all it can to make sure the market is well informed: they will raise, but given where we've come from the pricing in markets has gotten disjointed from underlying economies," he said. "Part of the problem we're getting into is the Fed has kept an eye on asset pricing and in my view far too firmly.
"Wall Street, in other words the market, has priced in a goldilocks view that rates will never rise. The markets should not be blaming the Fed in that case," he added.
