A House of Commons majority that rejects Theresa May’s proposed terms for leaving the European Union will show what Parliament is against but not what it is for.
This is because there is fundamental disagreement about what they want among MPs rejecting her deal: hardline Brexiters, Labour MPs who will vote against this Tory motion, MPs of diverse parties who want to remain in the EU, and Northern Ireland Democratic Unionist MPs who want to preserve the United Kingdom.
At this point a group of MPs will raise the cry: why not let the people decide in a second referendum?
Up to a point, winning a House of Commons vote is like winning a referendum. In both instances it requires a majority of votes.
A big difference is that in the House of Commons MPs can vote on amendments as well as a single question, whereas in a referendum there is normally a vote on a single dichotomous question.
But before a referendum could be held, the Commons must decide: should there be another EU referendum? if so, what would the question be?
The vote on whether there should be a second referendum splits MPs between a minority who see this as an issue of principle and a majority of pragmatic MPs whose views depend on what they think the outcome of a second ballot would be. In turn, the outcome depends on what the question is.
The 2016 referendum posed a choice between the status quo and change: Should the United Kingdom remain in the European Union or leave? It was fair then but it is now unsuitable because the status quo has changed.
The immediate alternatives are still: should the United Kingdom leave the European Union or should it remain? However, that question ignores the pragmatic question: what are the terms of leaving or remaining?
Three alternatives are clearly defined; each can be put as an amendment to a second referendum bill. The first is the no deal option, by which the UK would leave the EU without any conditions agreed with Brussels.
The second option is the conditions as currently agreed with Brussels by Theresa May and her team.
If Brussels accepts that the UK could withdraw its notification of withdrawal, the third alternative would the status quo ante: the UK remains a member of the European Union on unaltered terms, as though nothing had ever happened.
A variety of unicorn proposals (championed by the likes of Gove, Leadsom and Corbyn) that assume 27 European countries would modify their terms to mollify British MPs would be dead on arrival in Brussels.
Given three options, offering three choices on the ballot is possible, with the decision taken by a single transferable vote. When it was proposed in the 2011 referendum on changing how MPs are elected, more than two-thirds of voters rejected the principle of an alternative vote.
There is a pragmatic objection too: it is entirely possible that an alternative vote would endorse Theresa May’s deal as a lesser evil to a no deal Brexit or remaining.
But a precondition of holding a second referendum is that this would be just the arrangement that a Commons majority had rejected.
MPs would have to decide whether a second referendum ballot should offer two paths to Brexit, or a choice between leaving and remaining in the EU as before.
Principled Brexiters would vote against this because it would risk repudiating the majority verdict it won in 2016.
Pragmatists would be crucial in deciding what the wording of a second referendum ballot would be.
If Parliament rejects Theresa May’s deal in December, this would endorse the case for making the choice between remaining and taking back control by leaving without any conditions agreed with the EU.
Remainers could welcome this on the grounds that no deal has such fearful consequences that they would win a return to the previous status quo. But a campaign fuelled by Project Fear lost in 2016.
Any attempt to have a second vote on the possibility of remaining would mean a departure from the commitment of both Theresa May and Jeremy Corbyn to respect the decision of the 2016 majority.
The Cabinet bloc opposed to no deal as an economic and political disaster could tell Theresa May that her only chance of leaving office with dignity would be to back a second referendum offering two forms of Brexit: her deal and jumping off a cliff in twelve weeks time.
Pragmatic Tory MPs could find a referendum offering two Brexit alternatives doubly acceptable. It would meet their obligation to respect the will of the majority of Conservative voters in favour of Brexit whilst also offering businesses conditions and a timetable cushioning the shocks of Brexit.
Campaigners for a second referendum face the prospect of a bittersweet victory of having a referendum called without remaining being on the ballot, or a worse-tasting defeat.
A victory for the deal that Theresa May has negotiated with Brussels could be swallowed as a lesser evil to no deal.
However, a free and fair second referendum with the choice between the Downing Street deal and no deal would be like playing Russian roulette without knowing how many of the revolver’s six chambers are loaded with bullets.
Given the risks inherent in a second referendum, some pragmatic MPs will hold their noses and vote for the Theresa May’s deal in December to avoid waking up after a second referendum confronted by a future in the worst of all possible worlds.