Technology is also a popular suspect for lowering businesses costs and allowing companies to raise profits even as prices rise modestly, or even fall. There’s just one major hole in that argument. If true, labor productivity ought to have risen significantly when in fact it has been sluggish for years.

If any one, or a combination, of the offerings in this category were the culprit, the implication for monetary policy would be straightforward: As long as the phenomenon persists, keep rates a bit lower than you otherwise would.

3. Anchored Expectations

Our last category seems to be the Fed’s favorite person-of-interest. Fed Chairman Jerome Powell told Congress on Feb. 26 that “inflation expectations are now the most important driver of actual inflation.”

The theory suggests inflation outcomes are heavily influenced by what the public expects inflation will be, and those expectations can be anchored if the public believes the central bank will deliver on its target.

Proponents point out that U.S. inflation stopped responding strongly to unemployment in the early 1990s. That aligns with the widespread acceptance that the Fed was committed as an institution to keeping inflation at bay. Indeed, it’s been well behaved amid recent low unemployment and didn’t fall as much as expected when the jobless rate hit 10 percent in 2009. It seems inflation is not so much being held down as it’s being held in place.

Still, the case is largely circumstantial. Economists have only a loose understanding of how this functions in practice. Fuhrer at the Boston Fed is skeptical that in the real world people think about their expectations for long-run, aggregate inflation when setting prices.

The expectations theory, however, offers central bankers an attractive scenario. Once expectations become successfully anchored, they can worry less about ups and downs in the business cycle throwing inflation out of whack -- unless inflation expectations, themselves, drift off target.

And that’s exactly what’s begun to vex the Fed -- that the long stretch of sub-2 percent inflation may have caused expectations to decline. Thus its framework review this year.

“What we’re looking at is a way to more credibly achieve our existing symmetric 2 percent inflation target,” Powell told lawmakers.