One consequence of the first past the post system is that in a field of several candidates who could be successful it is essential for two of them to be able to convince voters that the real battle is between them and therefore voting for the others would not affect the outcome.
In 2010, Naomi Long famously convinced a broad spectrum of voters to tactically support her because she was best-placed to unseat Peter Robinson.
Nowhere in Northern Ireland is such a psychological battle more clear in this election than in South Belfast.
In that constituency political opinion is so widely divided that there are four candidates who could conceivably be elected - SDLP, DUP, Sinn Fein and Alliance.
The battle is likely to be between the outgoing MP, Alasdair McDonnell of the SDLP, and the DUP’s Emma-Little Pengelly.
However, the other parties who are conceivably able to win - Alliance and Sinn Fein - are attempting to convince voters that they are in the strongest position to beat the DUP to the seat.
For that reason, comments by veteran Sinn Fein figure Jim Gibney about the contest are intriguing because he does not say that voters should definitely back Sinn Fein candidate Máirtín Ó Muilleoir.
Writing in the Irish News yesterday, Mr Gibney commented on the situation in other seats where Sinn Fein is in the ascendancy, such as South Down.
Intriguingly, he then went on to say: “The story in South Belfast is similar in terms of the growth of the Sinn Féin vote set against the declining SDLP vote.
“But the contest there is much more difficult to predict. The seat is held by the SDLP and less than 1,400 votes separate all the contestants.
“The big concern for nationalists is to ensure the ultra-Brexit DUP do not take the seat. It is a fascinating battle. Will nationalists act as a group to hold the seat for nationalists?
“The judgement, and it is the finest to be made in all of the constituencies is, who is best placed to hold the seat: the SDLP or Sinn Féin?”
Campaign resuming today after attack
General Election campaigning will re-start today after two days in which party politics has been set aside in the wake of Monday’s atrocity.
Sinn Fein will launch an anti-Brexit document focused on the implications for farming of leaving the EU.
However, with the exception of Sinn Fein which has already done so, none of the major parties will be launching their manifestos until next week.
Now BBC and UTV debates back to back
Monday’s terrorist attack in Manchester led to the suspension of campaigning across the UK and the cancellation of what would have been the first big set piece of the election campaign in Northern Ireland, the UTV leaders’ debate scheduled for last night.
That has now been re-arranged, but will not be held until June 5 – just three days before the election.
That means that the UTV televised debate, which is recorded, will now go out the night before the BBC leaders’ debate, which was always scheduled to be broadcast live on June 6 – two days before polling day.