Certain Unionists have convinced themselves a referendum more than a year and half hence is already in the bag.

For Nationalists contending with disheartening polls, there could be worse news. George Santayana said it once and said it best: "Those who cannot remember the past are condemned to repeat it."

When you face the secessionist horde with smiting to be done, philosophy need not detain you, of course. Scottish General Election results, the impossible variety, can be set aside. A question such as "What happens if Scotland votes No?" can be dodged.

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A pretence is required for public consumption, but that's hardly a problem. So the entire Unionist camp has taken to promising splendid things for the Holyrood Parliament if independence is rejected. Marvellous "powers" will come our way, they say. But no-one, not a soul, will state precisely what those powers could or should be.

Instead, it's whack-a-Nat time again. On this occasion, the Scottish Government is accused of rank impertinence or delusive thinking – the charge sheet changes – for attempting to set out what might happen if the Yes campaign can win enough hearts and minds before the autumn of 2014.

The discussion paper, "Scotland's Future: from the Referendum to Independence and a Written Constitution", is ambitious, I'll grant you. It won't cause me to clear a space in my diary for March, 2016 – where independence has been pencilled in – just yet. I doubt, meanwhile, the document is exactly what the Electoral Commission had in mind when it called for clarification of the post-referendum process.

It's a start, though. It is certainly more substantial, in its attention to constitutional fundamentals, than David Cameron's refusal to "pre-negotiate Scotland's exit from the United Kingdom". John McCormick, the electoral commissioner, has said people want "factual information in advance about what will happen after the referendum". Mr Cameron's tri-partite side offer half-promises and not a shred of reliable detail.

Mr Santayana's famous remark becomes relevant. Anyone acquainted with the long history of devolution and home rule should have a fair idea of what Unionist promises tend to be worth. Either they are reneged upon – the Tories take the prize – or they come with a big, lethal catch. Tax-varying powers, anyone?

SNP ministers might be guilty of hubris, therefore, in sketching a post-referendum landscape. Michael Moore, the Scottish Secretary, certainly dismisses the exercise as an obsession with "process". But his own thinking – in a Scotland Office document entitled "Maintaining and strengthening the Scottish devolution settlement" – extends no further than Calman's inadequate recommendations.

Instead it is left to Willie Rennie, the Scottish Liberal Democrat leader, to revive the old federalist dream – whether England wants it or not – and propose that Scotland should raise two-thirds of its own taxes. Mr Rennie's power to deliver is about as certain as his power to persuade his Better Together partners to agree. The kite won't fly.

Labour's devolution reform commission meanwhile jumped into action last October, seven months after it was announced, but no further word is expected until the spring. The body will spend its time, in the words of Ed Miliband, "looking" at ideas. Beyond that, Johann Lamont's leader says only "there are other powers that we could devolve that should be devolved".

Elsewhere, a speech in January by Ruth Davidson, for the Tories, involved a comical volte-face. Having sworn to "draw a line in the sand" against further constitutional change, the head of Mr Cameron's Scottish platoon decided suddenly: "Change is coming and the Scottish Conservatives will be enthusiastic advocates for that change – the positive change that Scotland needs."

Ms Davidson did not define change, however, just as Ms Lamont has failed to define reform. Mr Rennie's speculative bid is equally opaque. Each of these three leaders is united (more or less) in the Better Together campaign. Their colleagues have been busy finding something risible in SNP plans for a written constitution. So why don't they just spell out the grand alternative?

It might be that too many voters remember their history. It might be, equally, that there is a logical flaw to all the chatter. Enhanced devolution – pick your own scheme – will not be offered on the referendum ballot paper. Why not? Because those talking up "more powers" wouldn't have it. They dismissed it as Alex Salmond's "consolation prize".

Now we are expected to believe the prize, or something like it, is available after all, but only if we decide to trust the No campaign. I might be wrong, but this doesn't sound much like the clarity John McCormick is seeking.

SNP ministers have probably been over-ambitious in naming independence month, but at least they have put something on the table. The document is otherwise perfectly reasonable. The Unionists who point to the opinion polls and ridicule a fantasy exercise should meanwhile keep an eye on the number of Scots – 20% by the latest count – who have yet to reach a decision.

They could also apply their minds to an honest search for a plausible alternative, but I don't hold my breath. Mr Cameron's refusal to engage, to "pre-negotiate", was only the latest example of the bad faith that has characterised the home rule story. Some of us have seen this movie before.

The Nationalists have made an opening bid. The Unionists are half-promising possibilities over which they denied the electorate a vote. Either they have no intention of delivering, or Mr Salmond will get his consolation regardless. Considering how much they detest the First Minister, I know where I'd put my money.

What quantity of "more powers" counts as sufficient, in any case? Without entering the realms of devo-this and devo-that, the yardstick to be applied to any Unionist offer is the extent to which, if sincere, it creates de facto independence. Is that really what all the Better Together noise has been about?

If so, a lot of Unionist people have misunderstood the argument. If not, they are being dishonest. Either way, they have never heard of George Santayana.