In Ireland, the pundit class moves like a herd. Nobody wants to get too far away from the conventional wisdom, even when the conventional wisdom settles around a nonsense idea, as it is today.

Fianna Fáil sources are now telling people that the party does not want to do business with Sinn Fein, and is minded instead to give Sinn Fein a chance to form a “coalition of the left”, involving that party, the greens, the social democrats, Labour, and people before profit, with some left wing independents. The idea is, apparently, that FF and FG will allow those parties to form a left wing Government, and that they will then sit back and wait for everything to go wrong, before surging back to power as the electorate turns to them as saviours.

It is an absolute fantasy.

For one thing, basic mathematics rules it out. The best that Sinn Fein can assemble in theory is about 60-70 seats. A left Government would therefore need either Fianna Fáil or Fine Gael to abstain. Fine Gael has already ruled this out, and Fianna Fáil seems to be ruling it out as well. But even if they reversed course, and did facilitate a left Government, it would be a terrible idea. Fianna Fáil should know this better than anyone.

If a left Government facilitated by Fianna Fáil makes a mess of things, FF will get a share of the blame. If it succeeds, FF will get none of the credit. What about the third option, where FF allows the Government to form, but opposes it on key legislation? Well in that scenario, FF is giving Sinn Fein a ready made narrative that things could be better, but FF and FG are using their majority to prevent meaningful change.

A left Government, in other words, is not some sort of cunning plan FF can employ to rescue their own fortunes. However it turns out, FF will then take a share of the blame.

The second reason the left Government idea is a fantasy is that the left will never agree to it. Paul Murphy and Richard Boyd Barrett are not going to enter a Government while the opposition benches are available to them. They would much sooner watch such a Government fail, and then make the case that only a “real” left Government can succeed. Close your eyes and imagine it – you can hear them now, bemoaning “the abandonment of left wing principles” and the “betrayal of the working class” the very moment a left Government fails to provide funding to the Dun Laoighaire women’s revolutionary art centre in the first budget.

The Greens and Labour and the Social Democrats won’t be keen either. The Greens because SF’s manifesto is fundamentally at odds with their own on climate policy, which is, at the end of the day, the only thing the Greens care about. An SF Government will have to lessen the burden of the carbon tax – the Greens want to increase it.

With only six seats each, Labour and the Social Democrats won’t want to risk the blame for everything that goes wrong in Government – and things always go wrong in Government.

The largest risk for the left from a “left government” is the third one, though, and it’s this: A left Government won’t be able to blame “right wing policies” for its failure. The Greens and Labour, respectively, have used this excuse to fuel their recoveries in recent years. “We were stuck in there with a right wing party”, they say. “We had to compromise”. The need for compromise is much lessened in a left coalition, and so the risk is much higher.

Nevertheless, we’re going to hear a lot about this fantasy in the coming days. It suits everybody to pretend that another option exists. Sinn Fein have to be seen to pursue it. The smaller left parties have to be seen to engage with it.

Fianna Fáil needs to be seen to be very reluctant to embrace Sinn Fein. The whole charade is necessary to spare everyone’s blushes.

In the end, the only numbers that add up are Fianna Fail and Sinn Fein, plus a couple of independents. It is that option, or another election.

When it comes down to it, Fianna Fáil will do what it always does – it will act in the best interests of Fianna Fáil, and announce that it is reluctantly acting in the national interest, by bringing in Sinn Fein and defending the rest of us from their worst excesses.

It’s inevitable. They just haven’t come to terms with it yet.