The Rubicon is the most-crossed river in Irish politics. Over the course of almost a century of independent democracy in the State, most fixed conceptions have become unfixed and most inconceivable arrangements have become conceivable.

The two-party hegemony has been eroded to accommodate coalitions, inter-party governments and a Rainbow spanning right and left.

Fianna Fáil has changed from being a party of single government to one that embraced coalition arrangements with the Progressive Democrats, the Labour Party and the Greens.

After an election it becomes a numbers game. For a party that wants to get into government it means getting the magic number of votes required (79 in the next Dáil). That numbers game has involved mergers when there have been Grand Canyon gaps between the dispositions of each party.

Back in 1992 most Fianna Fáil TDs opposed going into government with Labour but the numbers dictated it and it happened. Since the early 1980s government-forming possibilities have become more complex. It has been compounded by the substantial increase in Independent representation in recent years.

All the signs are that the number of non-party TDs and TDs attached to micro-parties could be in the mid- to high-20s. The 2011 election has left in its wake turbulent waters that will provide real headaches at the time of the next election. And the ongoing volatility in Irish political life will not have resolved itself in the 18 months before the next poll.

As a rule local elections are a poor guide to general elections. However, given the proximity of the next election, the following can be said with some degree of confidence. Both Fine Gael and Labour will lose seats. Perhaps the election of a new leader in Labour will help stem its losses, but only partially. The situation for both parties will not be helped by the reduction by eight in the number of Dáil seats from 166 to 158. Government TDs will be the losers in at least seven of the seats being extinguished.

Political instability

On a good day Fine Gael could still manage to hold on to 60-plus deputies, but Labour could fall to 15 or below. Fianna Fáil will undoubtedly recover but – based on the available evidence, it won’t be higher than the very low 40s. There’s no doubt that Sinn Féin will increase its tally – certainly into the 20s or mid-20s. The number of TDs from small left-wing parties or who are nonaligned will also increase to the 20s.

A number of arrangements could emerge from that situation. All of them would be radical departures from the norm. Some would lead to very unstable situations. And a number can be ruled out straight away. Fine Gael and Labour won’t have the numbers and besides Labour will probably want a period in which to regroup.

Fine Gael and Sinn Féin will never happen for reasons too obvious to state.

Even though Independents are large in number, the group is too diverse and fragmented to buoy up any government unless it is short a handful of votes. In that situation individual tailored deals will need to be struck.

If you are using Vulcan logic the two most obvious combinations are a grand coalition involving Fine Gael and Fianna Fáil, or a coalition involving Fianna Fáil and Sinn Féin. Both are radical departures and while they would provide stable government, both of them would have downsides.

A Fianna Fáil-Sinn Féin government is possible but would need to be shored up by Independents. Is it too early in the cycle? Will Sinn Féin leave too many hostages to fortune with its policy stances now? It could be damaged by too many U-turns, or the government could find itself locked very early into a series of interminable wrangles over policy. And that’s not to take account of the enormous political and historical baggage involved.

Or it may be that Fianna Fáil will find to its cost that for all its history and organisational strength it is still no match for the determination of Sinn Féin’s volunteers. It could find itself meeting the same cuckoo that nestled into the SDLP nest 20 years ago.

Revolving taoiseach

There are upsides. In Germany a grand coalition is going into its second term. It would provide stability and certainly there would be few ideological gaps.

Those who have cherished the notion that such a coalition would lead to a realignment of Irish politics might have their beliefs scotched – there is no guarantee the left will magic itself into a 50 per cent alternative when it has failed to do so for 90 years. Here, as in most EU countries, centrism is the name of the game. Harry McGee is Political Correspondent