The outbreak of the popular uprisings in the Middle East was unpredictable—regarding their timing, not regarding the underlying conditions that had been present for some time and that have powered the expressions of discontent. Once begun, much else about the wave of dissent and unrest has been uncertain: how far it would extend, and how much political change it will leave in its wake. But a couple of other observations about this region-wide phenomenon can be made with more confidence.

One is that the uprisings will not last indefinitely. No season goes on forever, and that is true of the Arab Spring. Even very discontented people do not revolt permanently; they eventually get too fatigued. Regimes get fatigued, too, of course. Which fatigue curve is steeper helps to determine whether an uprising results in significant political change. So the same phenomenon that we have seen grow since it started five months ago will also subside. At some time it will peak.

Another observation is that whenever the peak occurs, it will be difficult to recognize at the time. The regional revolt has no clear and simple real-time metric. This problem of interpretation and analysis arises with other phenomena as well. It often is unclear, for example, when a professional athlete has reached his peak. When a pro golfer goes for a long time without winning a tournament, is he past his peak or only in a slump? Major highs and lows in the stock market are even harder to recognize at the time. (If I could recognize them, I would have retired some time ago to manage my wealth.)

Looking at the most recent month or so of the Arab Spring, it is reasonable to start asking questions about peaks versus mere slumps. Plenty of action is still taking place, of course, mainly in three places: a civil war in Libya, the beginnings of an even more complicated civil war in Yemen, and protest being met with harsh repression in Syria. And given where things were left when Hosni Mubarak departed, we can expect in Egypt either more political change or more protest about the insufficiency of change. But lately poplar revolt has not been spreading. Places that earlier in the year looked as if they were on the verge of catching the contagion, such as Jordan or Saudi Arabia, seem to have escaped it.

And most recently one place that did catch it has taken a step back toward normalcy. Bahrain has ended martial law. One must quickly caveat the significance of this. Protests in Bahrain are by no means over, and the regime is not exactly relaxing (Saudi troops are still there). The regime also has economic and other reasons to promote an impression of normalcy that runs ahead of the reality. (One immediate objective is to get the promoters of a canceled Formula One auto race that was supposed to have taken place in Bahrain in March to reschedule the race.) Nonetheless, the lifting of emergency rule is hardly trivial, and it is a step normally associated with the subsiding of revolt rather than the escalation of it. It is a momentum-breaker, or at least could be seen as such.

Another factor making it difficult to identify which part of the curve of the Arab Spring we are at right now is the uncertainty of what the region will look like when the entire curve is done. Unlike with the pro golfer, whose skills we can be certain will eventually degrade to where he never can win any more tournaments, we don't know what the end state of the Arab Spring will be. The situation in the Middle East is even unlike the East European revolts at the end of the 1980s, which were tied together by the common thread of Soviet domination.

A more apt comparison is with the European revolutions of 1848, which like the Arab Spring involved diverse, mutually stimulating, uprisings across a region. One aspect of the 1848 events worth noting is that they resulted in inconsistent, and from the revolutionaries' viewpoint mostly disappointing, political change. A monarchy in France was overthrown in favor of the short-lived Second Republic, and peasant serfs in the Austrian Empire found some new freedoms, but other than that the yield was meager. Another aspect to note is that the uprisings, although significant enough in intensity and scope to warrant a major place in the history books, had pretty much run their course in the space of a year. And this was before the event-accelerating effects of social networks and other modern electronic media. Overlay the timeline of 2011 on that of 1848 and it is reasonable to ask whether we are getting close to halfway through this thing.

It would be foolhardy to declare that we are and that we have seen the peak of the Arab Spring, but it would be foolish not to admit the possibility that might be the case. Prudent policy, which has required being on the right side of history as the rebellions have ramped up, also requires adapting to events as they ramp down, especially if the political results are varied and disappointing and underlying grievances remain unresolved. And we may have to start doing that sooner than most realize.