“HE’S already stayed a lot longer than he wanted.” Barack Obama’s remark in a TV interview this week fuelled speculation that Ben Bernanke, whose second term as Federal Reserve chairman expires early next year, would soon leave the central-banking game. As Mr Bernanke laboured to communicate the Fed’s goals to journalists on June 19th, after the close of its policymaking committee’s latest meeting, who could blame him for longing to return to academia?

Since the Fed’s main policy interest rate fell to near zero in December 2008 it has deployed a complex array of “unconventional policies” to boost the economy. The Federal Open Market Committee this week ostensibly kept its foot on the gas. It promised to keep adding $85 billion in bonds per month to a stash that has almost quadrupled to $3.4 trillion since the beginning of the recession. It also pledged to keep short-term interest rates near zero.

Bond markets are more preoccupied by what lies in the future. Since late April the yield on ten-year Treasury bonds has leapt to more than 2.3% from 1.7%. Mortgage rates have also jumped; riskier assets such as emerging-market stocks have fallen sharply. This amounts to an effective tightening in monetary conditions, brought on by warnings made by Mr Bernanke last month, and reinforced at his press conference this week, that a “tapering” of the pace of asset purchases could get under way later this year.

Fed officials are doubtless annoyed by the market’s skittish reaction to the idea of tapering. In its view a more leisurely pace of buying does not amount to tightening. Fed economists reckon the size of the central bank’s balance-sheet is what matters most: so long as its asset pile is growing, policy is getting looser. By the Fed’s estimates, halving the monthly rate of asset purchases would be equivalent to trimming the federal-funds rate by five basis points per month instead of ten.

Furthermore, Mr Bernanke explained, tapering will be closely linked to economic conditions. If unemployment continues to drop and inflation behaves then tapering may begin later this year and continue in stages. If all went well, asset purchases would cease only by the middle of 2014.

Yet nothing is straightforward in central banking, particularly when its main interest-rate tool cannot be reduced any more. Expectations about future economic conditions, and the Fed’s response to them, become even more critical. When investors dial back their guesses at how large the central bank’s balance-sheet will grow, for example, bond yields rise. Similarly, a fall in expected inflation raises the “real” or inflation-adjusted interest rate. So if the Fed wishes to rein in quantitative easing (QE) without hurting the economy, it must convince markets it will not allow inflation to plunge or employment to stumble.

It is trying. The Fed this week linked the current round of asset purchases to the achievement of economic goals rather than a specific date or programme size as it had in the past. QE would continue, it said, until the outlook for the labour market had improved “substantially”. In his press conference Mr Bernanke clarified what that meant: a drop in the unemployment rate to about 7%.

Some market participants were reckoning on a more ambitious definition of “substantially”. Labour markets do look healthier now than they did late last year. Employment is growing at 194,000 jobs per month, impressive given the tax rises and spending cuts that have hit the economy. Unemployment has fallen from 8.1% last August to 7.6%, quicker than Fed officials expected when its third bout of QE began in September. Fed officials further lowered their projections for unemployment in the latest meeting. Yet the trend remains mediocre by historical standards; Fed projections put off a return to “full employment” to late 2015 at the earliest.

Adding to the Fed’s communication task is its multi-pronged stimulus approach. The Fed’s conditions for tapering on QE are separate from its conditions for keeping interest rates near zero: Mr Bernanke promised last December that rates would stay low at least until unemployment falls to 6.5%. Futures markets have rapidly brought forward their estimate of when the first rate hikes will occur to late 2014 (see chart 1), even though most Fed officials do not expect to raise rates until 2015.