Walter Laqueur is an American historian and political commentator.

IT IS DIFFICULT to predict revolutions. George Rude, the leading left-wing historian of the French Revolution once wrote that an intelligent observer of the French scene, native or foreign, would hardly have predicted in 1787 the coming of the revolution despite a variety of straws in the wind. There was probably no closer student of France at the time than Arthur Young, the leading British expert on agriculture, who visited France three times for extended periods on the eve of the revolution. While he saw a number of things that were wrong with the country, he certainly did not realize that a great revolution was coming.

Not as unusual as one might think. In Russia, there was no more ardent a protagonist of the revolution than Vladimir Ilich Lenin, who had devoted his whole life to the cause. And yet Lenin, in a lecture in Bern in January 1917, was quite pessimistic about the prospects of the masses rising up, telling his audience that the great event might not even happen in his lifetime. But it did happen just one month later. And by the end of the year, his party, the Bolsheviks, had taken power.

In our age it seems to have become even more difficult to make these sorts of predictions, perhaps because there has not been a revolution for a long time. The term is bandied about rather freely and carelessly. When I was asked many years ago to prepare the entry “revolution” for the Encyclopedia of the Social Sciences there was broad agreement that a revolution was something sui generis; today it seems to have become a synonym for rebellion, coup d’etat, mutiny, uprising and half a dozen other forms of upheaval. All too often we forget a once generally-accepted principle: namely that a true revolution involves a number of preconditions.

First, there is the spark needed to trigger the uprising. In 1917 it was a strike in Petrograd; the revolution in Munich in 1848 broke out because an umbrella had fallen (or was thrown down) from the top seats of a theater and the public mistook the noise for a gunshot; in Brussels in 1830 the performance of a romantic opera (La Muette de Portici) in which the aria of Masaniello, a Napolitan fisherman, denounced the injustices which had been committed by the Spanish Habsburg rulers, led to the division between Belgium and Holland.

In the case of the Arab awakening of 2011, 46-year-old policewoman Fedia Hamdi struck Mohamed Bouazizi, a Tunisian stallholder in a market, and in protest he burned himself alive (in the subsequent investigation it appeared that in fact Hamdi had not struck him—and she was acquitted). But there was enough tension and discontent within the country—and in particular with Zine el-Abidine Ben Ali—that had it not been for the unfortunate Bouazizi, some other incident might well have caused the overthrow of the regime....