An economy that is stimulated will eventually overheat. 受刺激的经济最终将会过热。

The central bank may believe that low unemployment is about to cause inflation. 央行可能认为低失业率导致了通货膨胀。

But the truth is that nobody is sure how far unemployment can fall before prices and wages soar. 但事实上没有人可以确定在物价和工资飙升之前，失业率能下降多少。

Not many years ago some rate-setters put this “natural” rate of unemployment at over 6%; the median rate-setter's estimate is now 4.7%. 就在几年前，一些利率制定者将自然失业率定在6%以上，但是现在他们估测自然失业率中位数仅为4.7%。

The only way to find the labour market's limits is to feel them out. 找出劳动力市场的限制因素的唯一方法就是去亲自体会它们。

Falling inflation and middling wage growth both suggest that these limits are some way off, for two possible reasons. 不断下降的通胀率和中等的工资增长都表明，这些限制因素多少有些不合实际，其原因有二。

First, higher wage growth could yet tempt more of the jobless to seek work (those who are not actively job-hunting do not count as unemployed). 第一，更高的薪水增长会吸引更多的失业者去寻找工作(不积极找工作的人不算失业者)。

The proportion of 25- to 54-year-olds in employment is lower than before the recession, by an amount representing almost 2.4m people. 如今25至54岁就业者的比率比经济衰退时期前更低，大约为240万人。

By this measure, which fell in May, joblessness is worse in America than in France, where the overall unemployment rate stands at 9.5%. 以这个方式来衡量，五月的就业率是下降的，美国的失业率比法国更高，整体失业率达到9.5%。

Second, even the moderate pickup in wage growth to date might encourage firms to invest more, lifting productivity out of the doldrums and dampening inflationary pressure. 第二，目前工资增长的明显好转可能会鼓励企业增加投资，来提升生产力以脱离不景气，减少通胀压力。

Jobs growth in America has already slowed from a monthly average of 187,000 in 2016 to 121,000 in the past three months. 美国的就业增长从2016年的月平均187000人已经减少到了最近三个月的平均121000人。

That is enough to reduce slack in the economy, but only just. 这足够减少经济的不景气所带来的影响了，但也仅仅是刚刚好。

Slowing it still further is needless so long as inflation remains quiescent. 只要通胀率保持不变，进一步放缓就显得不重要了。

It makes still less sense when you consider the asymmetry of risks before the Fed. 当你在美联储之前考虑到风险的不对称性时，它就没有什么意义了。

If tighter money tips the economy into recession, the central bank has only a little bit of room to cut rates before it hits zero. 如果货币紧缩政策导致了经济衰退，那么央行在其到利率零点之前就仅有一点点空间来削减它了。

But if inflation rises, it can raise them as much as it likes. 但是如果通胀率继续上升，央行就可以任意加息了。

This asymmetry of risks extends to the Fed's credibility. 这种风险不对称性延伸倒了美联储的信誉。

Inflation has been below 2% for 59 of the 63 months since the target was announced in January 2012. 从2012年一月美联储宣布这个目标以来，通胀率已经在63个月中有59个月保持在2%以下。

Continuing to undershoot the goal would cast more doubt on the central bank's commitment to it than modest overshoots would. 比起适度的超过，继续脱离这个目标会使央行遭到更多对其曾经承诺的目标的质疑。

For too long, hawks have made excuses for the persistence of low inflation. 长久以来，鹰派以很多理由来保持低通胀率。

The latest is to blame new contracts offering unlimited amounts of mobile data, as if cheaper telecommunications somehow should not count. 最新的一个理由是指责那些新合同提供了不限量的移动数据，似乎廉价的电信数据不应计算在内。

The Fed should keep its promise to base its decisions on the data, and leave interest rates exactly where they are. 美联储应继续坚守自己的承诺，它基于数据做出决定，并且保持利率精确的走向。