We don't often mark the anniversary of the day the Chairman of the Federal Reserve makes a particular remark, but we would guess that if we asked what phrasing Alan Greenspan made famous ten years ago today, more than a few people would come up with the answer irrational exuberance. (来源：www.EnglishCN.com)

Those people would be correct, of course; it was back on this date in 1996 that then-Chair Greenspan asked rhetorically "How do we know when irrational exuberance has unduly escalated asset values which then become subject to unexpected and prolonged contractions…?"

In other words, how can we central bankers tell when speculation fervor has enlarged a bubble to its bursting point? We’re not economists, but we would put our money on hindsight.

As far as we can discern, that speech ten years ago was the first and only time Alan Greenspan used the phrase irrational exuberance publicly. The phrasing captured the imagination of the public (no doubt in part because the bubble started deflating in the following days), and Yale professor Robert Shiller, who had testified in front of Greenspan two days before Greenspan made his speech, went on to publish a book titled Irrational Exuberance. Shiller did not lay claim to originating that phrase, however; in fact, he traced back Greenspan’s use of the similar (but not nearly as catchy) over-exuberance to 1959.