Some are launched by one group but hijacked by others, as in Egypt, where liberal democrats have become bystanders to the real contest between the army and the Muslim Brotherhood.
Some are born amid great idealism that quickly becomes a smokescreen for hypocrisy, as in the various communist uprisings.
Still others fizzle out, while a handful eventually produce new systems that, despite their flaws, really do change the world -- the French and American revolutions, for instance.
It's too early to know which trajectory will apply to the upheaval launched by Pope Francis, in part because at the level of structures and personnel he still hasn't made many sweeping changes, and in part because the parallels are inexact anyway -- Catholicism, after all, is a family of faith, not a political society.
Perhaps the lone certainty is that a revolution is, indeed, underway.
In mid-July, the Italian newsmagazine L'Espresso ran a cover story on the new pope under the banner headline "Ce la farà?" The phrase translates roughly as "Will he make it?" or "Will he pull it off?"
There was no need to explain what "it" meant -- everyone, it seems, knows that Francis is trying to engineer a Catholic glasnost.
Nonetheless, the expectation is that August will be a period of calm, after his taxing homecoming to Latin America for World Youth Day in Brazil, as a prelude to dramatic action in the fall.
It's thus a good time to stand back and ask a few big-picture questions:
- What are the main lines of the Francis revolution?
- What's already changed, and what's still to come?
- Who are those most put out by the changes -- who may seek to resist or reverse them?
- What are the looming moments that will determine how much change to expect, and whether it's for real?
Change is here
One could argue that in most of the ways that matter, the change has already arrived.
In just four months, Francis has revived the international prestige of the papacy and its moral capital.
The Italian edition of Vanity Fair recently declared him its "Man of the Year," including snippets of praise from unlikely quarters such as Elton John, who termed the pontiff "a miracle of humility in the era of vanity."
Polling in various parts of the world show approval ratings that would be the envy of any politician or celebrity.
A recent survey in Italy showed Francis' popularity at 85 percent, with spillover effects for the church; the percentage of Italians saying they trust the church was up to 63 percent, from 46 percent in January during the twilight of Benedict XVI's papacy.
"There has been a worldwide change in attitudes toward the papacy since the election of Francis," said veteran Vatican watcher Marco Politi, a columnist for the Italian newspaper Il Fatto Quotidiano.
"There has been a great outpouring of sympathy, not only among believers but also from people who are very secular or far from the church."
If anything, Politi may be understating it.
In terms of public opinion, Francis is already on the cusp of achieving the iconic status of Nelson Mandela, a figure of unquestioned moral authority. It's telling that during his trip to Brazil, protagonists in the nation's current unrest virtually tripped over one another in a contest to see who could demonstrate more deference and respect.
There's also a sense in which Francis is the "Teflon pope," in that nothing bad seems to stick.
When anything scandalous happens, reaction isn't to blame the pope, but to see it as additional proof of why he's needed.
Case in point: In late July, an Italian media outlet published reports that the pope's handpicked prelate to reform the Vatican bank had been involved in brazen gay affairs while serving as a Vatican diplomat in Uruguay more than a decade ago. Those inclined to take the reports at face value saw them as proof of a "gay lobby" that Francis will upend; those disposed to dismiss them said they're evidence that Francis' reform is eliciting resistance.
What everyone could agree on is that Francis is the solution, not the problem.
Truth to be told, most ordinary folk aren't paying attention to such inside baseball anyway. Vatican watchers may fixate on questions such as who Francis will name as the next cardinal secretary of state, or what changes he'll make at the Institute for the Works of Religion (the Vatican bank), but the only question most people have about a pope is, "Does he inspire?"
For now, the answer seems to be yes. Given all the scandals, bad press and controversy the Catholic church has weathered over the past decade, if that's not a revolution, it's hard to know what one would look like.
In Rome, too, there are clear signs that a new order has already arisen.
Clergy who chafed under what they perceived as a mounting liturgical fastidiousness during the late John Paul II and Benedict years -- showing up for a papal Mass, for instance, only to be told they weren't properly dressed because they weren't sporting enough crimson and lace -- report all that ended in mid-March.
Francis' humbler lifestyle is having a ripple effect.
Princes of the church today are more likely to be spotted wearing simple black clerical dress rather than the usual sartorial splendor, and some have begun to sign their names in official correspondence simply as "Don So-and-So," avoiding "His Eminence" or other bits of court nomenclature.
Even beggars who ply their trade around the Vatican have clued in that something has changed.
Vatican personnel say that if they spurn a request for spare change today, they're likely to hear back, "Cosa direbbe Papa Francesco?" -- meaning, "What would Pope Francis say?"
The game' is over
All that might be written off as superficial matters of style, but there's also a sense that the plates are shifting at a deeper level.
To take the most obvious example, there's long been an in-group/out-group distinction in the Vatican, between a majority who show up for work and try to do their job, and an elite minority who run "the game" -- who monopolize access to the pope, who control the allocation of personnel and resources, and who otherwise pull the strings of power on the basis of patronage and political savvy.
As recently as four months ago, this game was in full swing. Ambitious personnel knew precisely who they should try to befriend, which receptions to attend, which movements they should cozy up to, which devotions to embrace and so on.
Many Vatican officials found that repugnant, while others worked it to perfection, but in any event they knew the lay of the land.
Today, this insider/outsider distinction is largely defunct. By living in the Casa Santa Marta, by working the phone for himself, and by bypassing the usual gatekeepers, Francis has ensured that no one has a monopoly on his ear.
"He's very charming, but he's also very controlling, as all powerful people are," said Omar Bello, an Argentine Catholic journalist and author of a new book on the pope.
Efforts to descry a new cabal around the pope have been fruitless. In May and June, for instance, Francis was often seen in the company of Italian Archbishop Rino Fisichella, president of the Pontifical Council for Promoting New Evangelization, because of public events related to the Vatican's "Year of Faith."
Some thought Fisichella was emerging as a man of influence -- then, of course, Francis left Fisichella standing at the altar at a Vatican concert June 22.
What Vatican watchers have realized is that trying to figure out who's up and who's down misses the point. The novelty is that the game, as it has long been understood and played, is finished.
Over and over, Vatican personnel speaking on background say that Francis is his own man, collecting his own information and making his own decisions -- governing, in a sense, like the Jesuit provincial he once was.
There is no éminence grise, and no figure like Msgr. (now Cardinal) Stanislaw Dziwisz under John Paul or Msgr. (now Archbishop) Georg Gänswein under Benedict, serving as the power behind the throne.
With Francis, what you see is basically what you get.
Hallmarks of the new order
Four hallmarks of the new order seem clear.
First, this Latin American outsider seems determined to break the Italian monopoly on governance of the universal church.
Francis has set up three bodies to flesh out his reform: a group of cardinals to assist him in governance, a committee to investigate the Vatican bank, and a pontifical commission to study the Vatican's economic and administrative structures.
All told, they include 21 people now in positions of real influence, with just three Italians among them.
(As a footnote, one could argue that it's two and a half Italians, since the Italian named to the panel for the economic and administrative reform, a laywoman named Francesca Immacolata Chaouqui, is the child of an Italian mother and an Egyptian father.)
Beneath that is a calculation that de-Italianization is a sine qua non of reform, especially on the financial front. As one non-Vatican cardinal said to NCR on background, "If you want transparency on money, then you don't look to Italy as an example."
Second, Francis clearly wants to enhance the lay role -- not just in ceremonial ways, but in the nuts and bolts task of reforming the Vatican and governing the church.
His commission to study the economic and administrative structures, for instance, is made up of eight people, only one of whom is a priest -- Msgr. Lucio Angel Vallejo Balda, a Spaniard who serves as secretary of the Vatican's Prefecture for Economic Affairs, and who's a member of the Opus Dei-affiliated Priestly Society of Holy Cross.
The other seven are laypeople drawn from the worlds of economics, law and business management.
Logically speaking, this implies clipping the wings of the Vatican's clerical overlords.
In the Italian paper La Repubblica, journalist Marco Ansaldo called the commission a "complete subversion" of the Roman Curia -- noting, among other things, that its members don't report to the Vatican's power structure but directly to the pope.
Four months ago, if someone wanted to influence the Vatican's financial operations, they had to call an Italian cardinal. Today they'd be better advised to ring up a lay economist from Malta -- Joseph F.X. Zahra, who heads the new commission.
New accountability
Third, Francis is giving rise to a new culture of accountability, moving toward a more Anglo-Saxon understanding that "accountability" means somebody can actually get fired.
Two critical moves were the July 2 resignations of the top officials of the Vatican bank, director Paolo Cipriani and vice director Massimo Tulli, as well as the suspension in early June of Msgr. Nunzio Scarano, an accountant at the Administration of the Patrimony of the Apostolic See.
Scarano was shortly thereafter arrested in connection with an alleged plot to smuggle almost $30 million into Italy, and also faces a separate money-laundering investigation related to accounts he held at the Vatican bank.
Historically it was almost impossible for someone to lose a job in the Vatican, in part because of its tough labor protections, and in part because officials would insist that the church is a family rather than a Fortune 500 corporation.
Whatever the merits of that system, insiders say it tended to discourage potential whistle-blowers, because the perception was that wrongdoers would never suffer any consequences.
Scarano is a good case in point.
Insiders knew that his Vatican salary of roughly $2,000 a month couldn't possibly sustain his lavish lifestyle, which, according to Italian prosecutors, included a collection of artwork featuring pieces by Giorgio de Chirico and Marc Chagall.
Two Vatican officials who spoke to NCR on background, and who knew Scarano, said they always found something off about him, but never reported it because they didn't see any point. Both said that today they would have come forward.
Fourth, whether it's a matter of instinct or conscious strategy, Francis seems to be repositioning the church in the political center, after a fairly lengthy period in which many observers perceived it to be drifting to the right.
Veteran Italian journalist Sandro Magister recently observed, "It cannot be an accident that after 120 days of his pontificate, Pope Francis has not yet spoken the words abortion, euthanasia, homosexual marriage," adding that "this silence of his is another of the factors that explain the benevolence of secular public opinion."
Yet Francis has imposed no such gag order on himself when it comes to other political topics, such as poverty, the environment and immigration.
It's telling that for this first trip outside Rome, Francis chose the southern Mediterranean island of Lampedusa, a major point of arrival for impoverished African and Middle Eastern immigrants seeking to reach Europe.
The pope called for greater compassion for these migrants, chiding the world for a "globalization of indifference."
While the trip played to generally rapturous reviews, the anti-immigration right in Europe was outraged. Erminio Boso, a spokesman for Italy's far-right Northern League, said: "I don't care about the pope. … What I'd ask is that he provide money and land for these extra-communitarians," referring to undocumented immigrants.
The shift to the center also seems clear in ecclesiastical terms. In Rome, the perception is that power brokers associated with moderate positions, such as Cardinal Oscar Rodríguez Maradiaga of Honduras, coordinator of the commission of cardinals, are on the ascendant, while those linked to neoconservative or traditionalist stances, such as Cardinal Raymond Burke of the United States, head of the Vatican's supreme court, are in decline.
The church may not veer sharply in its political allegiances, but there seems a clear preference for the social Gospel over the culture wars.
These points alone are arguably significant enough to constitute a "revolution," but there's likely more to come, especially when the commissions tasked with studying reform report in.