The wisdom of the late Séamus Brennan holds the key to Sinn Féin maximising its potential in this election.
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Brennan was one of the country's most accomplished psephologists, analysing elections and voting statistics.
He was no soldier without practice to match the prattle. As Fianna Fáil general secretary in 1977, he studied the US presidential election, modernised campaigning here and helped deliver the largest majority ever gained by one party, under Jack Lynch.
One of Brennan's maxims about election counts was when a party was on the up, it benefited both from number one votes and transfers.
"When you're popular on the first count, you don't suddenly become unpopular on the second. And when you're unpopular, you stay unpopular," he would say.
'Brennan's Law' dictates that a party benefits from transfers when they are already up on the first count.
Our political system isn't perfect. The PR-STV, multi-seat constituency model is awkward. But it does give smaller parties an opportunity to achieve parliamentary representation. The system can throw up strange results on an individual constituency level, but tends to even itself out across the board.
Sinn Féin is not running as many candidates as it should be to capitalise on the sudden spurt in its support.
However, that doesn't mean Mary Lou McDonald's party won't be able to convert votes into TDs - and those seats present a path to power.
At the last general election, Sinn Féin won 23 seats off the back of 14pc of the votes. The party won one more of the 158 seats than their share implied, known as a seat bonus.
In this election, Sinn Féin's support is registering around the 25pc mark in opinion polls.
Roughly, for every five voters the party had in the last general election, it now has nine.
Getting a quarter of the votes should imply the party wins a quarter of the seats - 40 of the 160 TDs. But Sinn Féin will have a disproportionately high vote in some constituencies. McDonald herself in Dublin Central, for example, is likely to have close to enough votes to win two seats, but has no running mate. The same scenario will play out in strongholds like Dublin South-West, Dublin South-Central and, potentially, Dublin North-West. Sinn Féin will lose out on extra seats as a result.
The party will probably pick up extra seats though in Donegal and Cavan-Monaghan, with two candidates, and hold its doubles in Louth and Dublin Mid-West.
Across the rest of the country, you also have to expect they will hold existing seats on the back of the Shinner surge.
From there, you start to look at where it can make more gains. Look at it this way, Sinn Féin will have 80pc more votes than the last general election.
The starting point is where there is a base from the last general election.
Dublin West and Galway West fall easily as large urban centres. Next comes the bounce of the ball in Wexford, Mayo and Meath East. Then the longer shots like Dublin Bay South, Meath West and Kildare South.
The prevailing wisdom is that's it, end of story, the supposed 'Shinner Summit' is about 30 seats tops.
Here's where 'Brennan's Law' kicks in. Sinn Féin candidates will be more transfer-friendly than in the past. The rule of thumb is you need to be on about 60pc of a quota on the first count to win a seat.
Independent minister Katherine Zappone performed a minor miracle last time by winning off just 40pc of a quota.
Although much is made of the role of transfers, they rarely enough help candidates leapfrog the field from way down.
New academic research shows if you're not in contention on the first count, you don't tend to win the seat.
'The Transfers Game', by Stephen Quinlan and Hannah Schwarz, studies elections for the Maltese parliament, Scottish Assembly, Northern Ireland Assembly and the Dáil.
"We find that on average transfers are pivotal in the election in one of 10 election candidates," the academics say.
Sinn Féin candidates will be getting a raft of votes they have never seen before as the party brand kicks in dramatically.
No-hopers are suddenly believers.
Assuming the candidates can do enough in the first count to get into contention, transfers can help.
Now the longer-shot seats come into play, particularly if there is a vulnerable opponent. Cork South-West certainly matches that description.
On Dublin's leafy southside, Dún Laoghaire and Dublin Rathdown, the Sinn Féin candidate will be in the mix.
Likewise in the Lough Derg Triangle of Clare, Tipperary and Galway East. And finally, Limerick County and Roscommon, there will be a Sinn Féin candidate in the shake out.
In all these cases, the Sinn Féin candidates will have to outperform even their national swing to win a seat.
Let's be clear, the party won't win all these seats, but their number of TDs can be in the high 30s, tipping over 35 seats.
That's assuming the party can hold its support. Sinn Féin has a bad habit of over-performing in polls. At the last general election, they dropped six points in the last nine days of the campaign.
Even if it only retains half its newfound support, it's still heading for 30 TDs.
The next assumption of the 'Shinner Summit' is it can't lead a government. Why not?
On the back of a mandate for change, it will be duty-bound to seek to put a coalition together. Add Sinn Féin, the Green Party, the Labour Party and Social Democrats and you'll be heading for 55 to 60 TDs. That's more TDs than made up Enda Kenny's coalition four years ago.
The Greens, Labour and Soc Dems won't want to be seen to rule out the Sinn Féin option, in favour of Fianna Fáil, after the voters demanded "change".
After that, it will be up to Independents and other parties to decide which way to go.
It's a long way to get to the 80 TDs needed for a majority, but the realignment of politics after the crash is creating all sorts of new scenarios.
It's certainly an unstable arrangement, but so too are many coalitions. Confidence and Supply wasn't expected to last six months.
But the voters won't thank the politicians for going back for a second general election if there are options.
Mary Lou for Taoiseach: don't rule it out before a vote is cast.