Sometime next year, the Federal Reserve will likely face an unusual confluence of economic circumstances. One of its mandates, full employment, will call for monetary policy to tighten relatively quickly; the other, inflation, will suggest it should stay loose. How should the Fed weigh these competing goals? It may want to dust off a doctrine from the 1990s, “opportunistic disinflation” and rechristen it "opportunistic inflation.”

The impressive pace of job creation reported today underlined the approaching crunch point. The number of new non-farm jobs in November, at 321,000, was the most in nearly three years. Along with revisions of 44,000 to prior months, it shows this year’s already-solid pace is accelerating. The unemployment rate remained at 5.8%, but if this year’s combination of job and labour force growth continue, it will drop below 5% within a year, easily undershooting the Fed’s estimate of its natural rate. True, the current unemployment rate may overstate how strong the labuor market is, but other measures suggest slack is quickly disappearing: the broader U-6 measure of underemployment dropped to 11.4% in November, from 11.5%, long-term unemployment edged down to 1.8% from 1.9%, and involuntary part time work declined.

But even as the Fed hits its full-employment target, it will be badly missing on its 2% inflation target – from below. Headline inflation was 1.7% in October, and core inflation, according to the Fed’s preferred index, was just 1.5%. Petrol prices have plunged further since, so headline inflation is likely headed below 1%, and pass-through effects will likely push core further down as well.

The view inside the Fed is that this undershoot is temporary and over the next few years, a strengthening economy and inflation expectations will tug inflation back to target. They shouldn't be so sure. The fall in the oil price is a mixed blessing. It will generate a powerful lift to consumption and employment in the next six months, and indeed may already have, given the strength of retail employment. But, along with the rise in the dollar and the fall in other commodity prices, it will keep inflation below target for several years. Inflation has already persisted below target longer than the Fed expected, and the latest data suggest that it is the public's expectations of inflation that are converging towards actual inflation, rather than the other way around.

This makes it all the more likely that expectations, and thus actual inflation, will become entrenched below target. Against a backdrop of full employment, this may seem acceptable. It isn’t. Too-low inflation means that the next time the economy falls into recession, interest rates will once again probably fall to zero, which may be too high in real terms to adequately restore growth. The risk, then, is that inflation grinds even further below target. While the circumstances facing the Fed may be novel, the tactical challenge is not. Two decades ago, inflation was above any reasonable definition of price stability. In contemplating how to get it lower, Fed officials came up with the moniker of “opportunistic disinflation.” The Fed would not deliberately push the economy into recession, but it would exploit the inevitable recessions and resulting output gaps that came along to nudge inflation closer to target. In 1996 then governor Laurence Meyer defined it thus:

Under this strategy, once inflation becomes modest, as today, Federal Reserve policy in the near term focuses on sustaining trend growth at full employment at the prevailing inflation rate. At this point the short-run priorities are twofold: sustaining the expansion and preventing an acceleration of inflation. This is, nevertheless, a strategy for disinflation because it takes advantage of the opportunity of inevitable recessions and potential positive supply shocks to ratchet down inflation over time.

The strategy succeeded: after the recession of 2001, inflation fell to 2% and stayed there.

Today's mirror image would be “opportunistic inflation”: exploit any overheating in the economy as an opportunity to push inflation higher. If unemployment does fall to 5% next year, that should have two beneficial effects for the labour market. First, it should push up wages. Hourly earnings rose 0.4% in November, an unexpectedly brisk and long overdue increase. But they are still up just 2.1% from a year earlier. Since profit margins are so wide, it will take several years of stronger wage growth to generate cost-push inflation. Second, some of the long-term unemployed who have quit the labour force should be drawn back in, reversing some of the loss of potential output brought about by the prolonged period the economy spent depressed.

To get inflation higher requires a negative output gap by allowing unemployment to fall below its natural rate for a time. That may happen even on the current plan in which interest rates start to rise slowly from zero in 2015. If so, the Fed should simply let it happen. It may want to encourage the process by delaying the normalization of rates, or stretching it out over more months. This is not without pitfalls; inflation could take off more quickly than expected, or financial imbalances could worsen. On the other hand, inflation may stay dormant for longer, and the Fed will then conclude the natural rate of unemployment is actually lower than 5%; and it will have been glad not to have tightened too soon.