Tánaiste and Progressive Democrat leader Michael McDowell tonight firmly ruled out joining Fine Gael, Labour and the Greens in a rainbow coalition after the next election.
Mr McDowell said a four-sided coalition would be a monumental cheat on the electorate and a recipe for political disintegration.
"We will campaign against the creation of such an unstable and incoherent government," the Tánaiste said.
"We will not join or support such a government because we believe that a second election would be preferable to the establishment of a non-viable Rainbow Government which flew in the face of the mandates sought by the parties in it.
"The Progressive Democrats will not be joining a FG/Labour-led coalition, or a FG/Labour/Green-led coalition."
Mr McDowell said it would destroy the very reason for the PDs' existence. But he said his party would consider siding with either Fine Gael or current government partners Fianna Fáil.
In an address to party faithful in south Dublin, Mr McDowell insisted a pact could only be made with a party of similar ideologies and warned he would head for the back benches rather than take up office just for the sake of it.
"The Progressive Democrats will contest the next election as an independent party that remains prepared to govern with either of the parties with which it is ideologically compatible," he said.
Unsurprisingly he also rejected any possibility of a link-up with Sinn Féin. "For the purposes of completeness, I want to re-iterate tonight what I have clearly stated on many previous occasions. The Progressive Democrats will not support or participate in a government which is dependent on the support of Sinn Féin deputies."
Mr McDowell said over the last few weeks, as Labour leader Pat Rabbitte continued to face searching questions on his post-election tactics, there was growing evidence the Rainbow alternative is a failed political enterprise.
He said the Labour/Fine Gael Mullingar Accord, with or without the inclusion of the Greens, did not have the support of voters.
Mr McDowell said even with the inherent differences the three had on economic outlook they were also hugely split over neutrality, immigration and taxation. But he accepted a Labour/Fianna Fáil coalition was a real possibility and called on Mr Rabbitte to set out his stall.
"The attention of the people is increasingly concentrated on a far more likely scenario - namely, whether the next Government will be a coalition between the Progressive Democrats and Fianna Fail or a coalition between the Labour Party and Fianna Fail," he claimed.
"Understandably in that context there is an appetite for clarity from party leaders."