LONDON — A second referendum on Britain leaving the European Union is considered likelier than ever.
It’s not just because Jeremy Corbyn, the leader of the Labour Party, has asked for a parliamentary vote on whether to hold a new referendum.
Even many members of the ruling Conservative Party, possibly including Prime Minister Theresa May, seem to be following through on Brexit more out of a sense of democratic duty than actual conviction.
Two and a half years ago, 52 percent of British voters, 17.4 million people, voted to leave the bloc. But public opinion has flipped, with a slight majority now saying they would prefer to remain.
Still, for all the momentum for a second referendum, there are some reasons for Britons on any side of this issue to be cautious.
Referendums are not particularly democratic.
The most basic form of democracy? Think again. There is widespread agreement among political scientists that referendums are messy, dangerous and not nearly as democratic as they seem.
Back in 2016, we asked Michael Marsh, a political scientist at Trinity College Dublin, when referendums were a good idea. “The simple answer,” he said, “is almost never.”
“I’ve watched many of these in Ireland, and they really range from the pointless to the dangerous,” he said.
Nothing Professor Marsh has seen in the years since the Brexit vote has given him reason to rethink that view, he said this week.
Referendums tend to be volatile, turning on unrelated political swings — or even the weather, which is thought to have helped swing Colombia’s 2016 referendum on a peace deal with insurgents.
And they are poor tools for measuring public opinion. When a referendum is put forward by the government, for example, people often vote in support if they like the leadership and in opposition if they dislike it, according to research by Lawrence LeDuc, a political scientist.
Raw majority will is not the same thing as democracy, particularly when that majority is slight. Democracy is meant to function through voting, yes, but also through representative officials and independent institutions intended to protect the common good.
“The idea that somehow any decision reached anytime by majority rule is necessarily ‘democratic’ is a perversion of the term,” Kenneth Rogoff, an economics professor at Harvard, wrote after Britain’s 2016 vote.
Referendums that pass or fail by an overwhelming majority, like Ireland’s recent vote to repeal a constitutional amendment that banned abortion, can be more reliable. Wide margins leave little space for outside factors to swing the outcome. And they create a perception of consensus, however artificial, that helps all sides accept the results.
Crucially, the Irish referendum, which was approved by 66 percent of the voters, merely removed a limit on lawmakers’ authority, freeing them up to act as they wished. That gave both voters and elected representatives a say.
The Brexit referendum, by contrast, demanded a specific policy outcome but offered little clarity on how to achieve it.
A second vote could actually undermine faith in British democracy.
One reason political scientists are so skeptical of referendums is that leaders tend to turn to them as a sort of political theater. They give the appearance of democracy happening when those leaders are unable to get what they want through the regular legislative processes.
“A referendum is not a form of direct democracy,” Nadia Urbinati, a Columbia University scholar of democracy, said. “A referendum is used when a representative system decides that it wants to have the support of the people.” And usually, it’s for something the government has already decided to do.
That can backfire, though, as Prime Minister David Cameron learned in 2016 when he called for a Brexit vote. Mr. Cameron did so not because he was curious what voters thought, but because he believed they would vote to remain, shoring up his position within the Conservative Party, political analysts widely believe.
If a second referendum results in a narrow majority for remaining in the European Union, then the nearly half of the country that still wants to leave could reasonably conclude that the political establishment ginned up a new vote to suppress the popular will that was expressed in 2016.
But if the public once again votes to leave, then the people who wish to remain — and thought that a second referendum would deliver that — may doubt whether the outcome was truly democratic. After all, polls have shown for some time that a slight majority favors staying in the European Union.
Either way, nearly half of the British electorate is likely to come away feeling as if a second referendum cheated them out of a voice, rather than granting them one.
This could worsen one of the gravest problems facing British democracy, and Western democracy more broadly: plummeting faith in the political system, which has fractured political parties and paralyzed governments.
A vote on what, exactly?
And then there is the problem of what to put on the ballot.
One option is a ballot asking voters to choose between the withdrawal deal Ms. May proposed that was rejected by Parliament — a so-called soft Brexit, with some ties to the European Union — and a no-deal Brexit, in which the country leaves the bloc with no arrangement for how to do so. That is favored by hard-line Conservatives.
This would help settle which form of Brexit to take, but not whether to leave the bloc at all.
Another possible ballot would present a choice between Ms. May’s deal or staying in the European Union. But this wouldn’t be very representative, excluding Brexit supporters who want a different deal than the one Ms. May struck.
A true do-over, repeating the same question from 2016, if it returned the same result, would do almost nothing to resolve the current political deadlock, which is over what form of Brexit to have.
Adding more options to the ballot could risk creating new forms of uncertainty.
Imagine a 30-30-40 split between Ms. May’s deal, a no-deal Brexit or staying in the European Union. That would count as a win for remaining, even though 60 percent of the voters would have gone for leaving.
Ballots that include multiple questions or allow voters to rank their preferred outcomes could be just as messy.
And any ballot will have to be approved. With Parliament as divided and dysfunctional as it is at the moment, agreeing on something this fraught could be difficult.
Even if lawmakers could agree on a ballot, boiling a complex policy question with dozens of possible answers down to a simple yes or no can create more confusion than clarity.
“There is the tendency to see a plurality as single minded,” Professor Marsh said. In reality, he said, in a choice between yes and no, “there may still be very many who want something in between that.”
That was one lesson of the 2016 referendum.
Many of the voters who selected “leave” had very different — and mutually exclusive — ideas for how that would work. This helped feed chaos in Parliament, where there might be a slight majority for some fuzzy idea of Brexit, but no majority for any of the actual plans.
A close vote could force the least popular result.
To hear some “remain” supporters talk, you would think that their side is all but guaranteed to win a second referendum. But polls are still close enough that voters could narrowly affirm the 2016 decision to leave.
If that happens, then it will become much more likely that Britain ends up with a no-deal Brexit.
There would be less slack from an impatient European Union and less maneuvering space for humiliated Brexit soft-liners. With a stronger mandate to leave but no ready plan, Brexit hard-liners could push through a no-deal withdrawal.
Analysts believe that a no-deal Brexit would most likely crater the British economy, causing significant suffering, particularly among the poor, whose social services have already been shredded. There could also be food and drug shortages.
A no-deal Brexit is the least popular of any of the possible outcomes, polls generally suggest — and yet a second referendum could bring it about. An odd outcome, but a plausible one, for a process meant to enshrine popular will.
A referendum may look appealing to certain constituencies, particularly those who want the hardest possible Brexit or those who want to keep Britain in the European Union.
But whoever wins, it’s hard to argue that British democracy itself would come out ahead.