Despite having invented it, the ancient Greeks took a dim view of history.

The pettifogging details of who did what, where and when were, for many, of limited importance. A more elevated form of understanding the world, they believed, was mythology, in which the things described may not, strictly speaking, actually have happened, but in which the narrative demonstrated profound and eternal truths which were universal.

The Alexander de nos jours has adopted this attractive model of describing reality, but with the novel innovation of applying it to the future. One can see why this tactic should appeal to the First Minister. The primary purpose of his party, after all, is to bring about the creation of a new state (since I don't think anyone is arguing that we revert to the constitutional arrangements of 1706). And because no-one knows what will happen in the future – unless the Mayans were right, in which case it won't matter because there won't be one – it is understandable that the Nationalist speculations should put the most favourable gloss on what might happen.

Myth and fiction are the very things for creating a country – great chunks of what we think of as typically Scottish were made up by Sir Walter Scott. But they're less effective when it comes to creating a state. This is where history, with its disappointing insistence on facts, scores over prophecy. You can know the past as you can never know the future.

Still, what matters for Nationalists is that you can change the future. So, in Mr Salmond's imagination, an independent Scotland will be one of the richest OECD countries, a full and valued member of the EU, a partner in determining the monetary policy of the Bank of England, a high-tech knowledge economy and a manufacturing titan which will easily be able to afford the kind of generous social welfare provisions provided in Scandinavian countries with income tax well over 55%.

None of these objectives is impossible, even if I don't happen to think that they're very likely or, in some cases, even desirable. In order to bring something about, you have, after all, first to imagine it. Then you need to believe it is possible, and persuade others of that, and then take the necessary steps to bring it about.

It is in these niggling further actions that the mythological approach runs into trouble. In order to persuade their fellow countrymen and women that their vision is (a) realistic, (b) desirable and (c) achievable, the SNP line has been to portray hopes, aspirations and, alas, some outright fantasies as statements of fact when they are more like articles of faith. And in recent weeks, when these yarns have been picked at, there has been a distressing amount of unravelling.

The first point is the – one would have thought, rather important – question of whether Scotland would remain in the EU. As many people have pointed out, this was always going to be a political question, and not a straight constitutional or legal one. That need not have damaged the SNP case; a Scotland which had voted for independence would be fairly likely to get into the EU, and it is not altogether inconceivable that it might get in before independence negotiations were completed (which is Mr Salmond's new line).

What was tactically daft was to insinuate that the issue was all but settled when no-one had bothered to look into it. Even if there had been an opinion, and a favourable one, anyone could have guessed that other opinions and political interests might get in the way.

It's the same story with the plan to keep the pound, adopted when it became clear the euro was going down the pan. Of course any country can peg its currency to someone else's (the newly independent Lithuania, for example, pegged the litas to the US dollar, and later to the euro), but it essentially means abandoning control of monetary policy. To imagine that the Bank of England would consult Holyrood about it is as fanciful as imagining that the Federal Reserve Bank would ring up Vilnius before bailing out Fannie Mae and Freddie Mac.

Since a man with half an eye can see that, why go around telling people there is a "dialogue"? Technically, I suppose there's a dialogue if I say to you: "Could I have a word about borrowing a fiver?" and you say: "Get knotted", but it's not what you'd call a meaningful dialogue.

Similarly, the claim that we'd be the sixth-richest OECD country, which Nicola Sturgeon repeats as if it were part of the Nicene Creed, might, I suppose, be true – though I can only make the arithmetic work by imagining that we inherit none of the UK's deficit but all its oil reserves, and then nationalise them. But it is a silly strategy to tell the electorate that what you hope will be the case is already a proven reality – especially in the total absence of proof.

Asking whether we might be unable to rejoin the EU, or forced to adopt the euro, or introduce border controls (because of the Schengen requirements for acceding states), or retain the British vetos and rebates or a thousand and one other questions is not scaremongering. It is a simple attempt to establish the hard reality of the situation.

The disappointing thing is that the whole raison d'être of the SNP should have led them to formulate plausible answers to these questions. It may be that they can be answered, or even that the answers would persuade the electorate that independence is the way forward. I doubt it, because I suspect that even if one could prove an independent Scotland would make everyone better off, they would still be swayed by the more intangible bonds which link the nations of the United Kingdom.

But I don't know, precisely because these bonds are intangible. There is, however, no point in pretending that national sentiment or patriotic ambition are the same sort of thing as treaty obligations or international trade agreements. I grant you the facts may be hard to obtain. I can even just imagine (I have a very fanciful imagination) the facts supporting the SNP's case.

What I can't imagine is why anyone would lend their support to a party that we now know hasn't even bothered to check any of its assertions. Mr Salmond may think history is for making, but that's not the same as just making it up as you go along.