Their September forecasts for the central bank's key rate range from less than zero to 3 percent by the end of next year, and from 3 percent to 4 percent in the long run.
Yellen, Fischer and others at the Fed insist that any tightening is likely to be gradual. Policymakers acknowledge, however, that they have yet to agree what gradual means and this uncertainty has been reflected in increased volatility in short-term Treasury markets in recent months.
Trail of tears
Fed policymakers say confidence that inflation will rebound should be enough to pull the trigger on rates for the first time, most likely at their Dec. 15-16 meeting. The second move may need more proof that prices are in fact rising, so its timing will offer a better clue to how the tightening cycle will unfold.
It may also show to what extent the Fed still relies on the theory of an unemployment-inflation trade-off commonly known as the Phillips curve.
"You hear arguments inside and outside the (Fed's policy) committee that in this circumstance you should just look at inflation by itself," Bullard, who will vote on rates next year, said. "Maybe it is the appropriate thing to do in this environment,(but)if we are really going to give up on the Phillips Curve at the heart of central banking that would be a major change," he told Reuters from his St. Louis office.
San Francisco Fed President John Williams, a Yellen ally, argues there is a "strong case" for a December rate rise. But he has warned that declining estimates of neutral rates — those that neither accelerate nor slow the economy — are a "red flag" that the economy could have become more vulnerable.
The very fact that the Fed is debating a tightening while Europe, Japan and China continue monetary easing, is giving some policymakers, such as Fed Governor Lael Brainard or Chicago Fed President Charles Evans, a pause.
One fear is a repeat of what happened to the European Central Bank and Sweden's Riksbank. Both raised rates in 2011 because of inflation concerns only to reverse those the following year when a nascent recovery went into reverse.
"We have had different points in time since the downturn where certain regions of the world thought they could de-link against the rest of the world," Evans said this month. "There's often a trail of tears that follows that hope that their own area is stronger."