A YES vote, Alex Salmond told the SNP conference, would be "above all, an act of national self-confidence and self-belief".

I don't find that difficult to believe. If the Scottish people vote for independence, it could hardly be described as anything other than, first and foremost, an act of self-belief. But, despite the upbeat mood of the Nationalist conference - which is entirely understandable, since many of the delegates will have been working for decades for the vote which is now less than a year away - all the polls continue to suggest that most Scots don't believe in voting Yes.

And while voting Yes may automatically indicate self-belief, voting No does not suggest any commensurate lack of self-belief. Nationalists are often keen to imply that those who would prefer to remain part of the UK think that Scotland couldn't function (or at any rate, function well) as an independent nation. But it isn't necessary to believe that at all to be a Unionist; indeed, I imagine very few Scots think anything of the sort.

The majority, to judge by the polling, have no trouble having faith in Scotland, and even, apparently, the SNP - the Holyrood Government's most recent approval ratings are +23, compared with the Westminster Government's -28. Nor have they any hesitation about primarily identifying as Scots, as more than 80% of us say we do. It's just that they don't believe in separation from the rest of the UK.

Of course, the aim of the Yes campaign is to get them to believe in it, and therein lies the difficulty for proponents of independence. Though they continually attack their opponents for "negativity", the pro-independence lobby is, if anything, rather more guilty of scaremongering.

A few of those who oppose the break-up of the UK may do so because they are happy with the status quo. It's more likely, however, that while not entirely satisfied with it, they think that independence is the wrong remedy. But those who want independence have, by necessity, to define their programme by distinguishing it from the current arrangements. Nicola Sturgeon, for example, told the conference that a No vote would trigger deeper cuts by Westminster and endanger benefits available to Scots, but not offered elsewhere in the UK - ignoring the fact that they were all introduced without independence.

It also puts the SNP in the awkward position of setting out a list of things which an independent Scotland could have; repeal of the "bedroom tax", an increase in the minimum wage, cuts to fuel bills, renationalisation of the Royal Mail, in addition to maintaining free bus passes, tuition fees, prescription charges, care for the elderly and so on.

The problem here is not whether you believe this is desirable, or even affordable. It is that none of it is really within the scope of the referendum question, because the question isn't "Would you like a Nordic-style social democracy free from the colonial jackboot of cruel English Tories?" It is just "Should Scotland be an independent country?"

In reality, Mr Salmond is well aware of this and, when pressed, perfectly honest about conceding the point that, in the event of a Yes vote, all these theoretical policies will be a matter for the Scottish government elected after the referendum. But, as his slight shift in position over the timetable for the removal of Trident makes clear, it's not always straightforward to distinguish between the SNP's proposals and what might, or might not, happen in an independent Scotland. However unlikely he, or I, may think it, in theory, Scots might even elect a government which wanted to keep Trident.

I have some sympathy with the Nationalists about this, because they are damned if they do spell out their plans, and damned if they don't, but I fear that next month's publication of the White Paper setting out a prospectus for independence will not resolve this fundamental dichotomy. The burden of proof is on the Yes campaign to provide, at the very least, evidence that Scotland could be independent. And though there may be disagreement on whether their view is excessively optimistic, I don't think anyone doubts that some such figures will be forthcoming.

But even if the White Paper's proposals and costings were accepted by everyone, they would present no more than the information the Scottish electorate deserves in order to make a decision. The case for independence will still have to consist of describing what might be, but which cannot be guaranteed - just as, of course, the case for a No vote necessarily consists of pointing at what is already present, and describing things which might possibly be lost.

In any case, you could produce figures which suggested independence would be disastrous without dissuading diehard Nationalists, or costings which suggest Scotland would be richer per capita than Qatar without winning round convinced Unionists. That, on the whole, strikes me as rather a good thing. Not because the evidence is unimportant - on the contrary, the voters are entitled to it - but because the debate on the economics of independence, or indeed of the kinds of policies which distinguish Scotland from the rest of the UK, are all things which are open to interpretation and to change.

A cast-iron manifesto undertaking on, say, university tuition fees may later be abandoned, as anyone who voted Liberal Democrat can tell you. A claim to have abolished boom and bust, such as the one Gordon Brown made, may turn out only have abolished the first bit.

If you're an advocate of devo-max or plus or anything else, the referendum offers no clue about whether you're more or less likely to get it if you vote No. But nor does a No vote affect in any predictable way the chances of greater welfare cuts, a Labour government, a rise in living standards or anything else.

Similarly, a Yes vote offers no guarantee that the sort of programme the SNP is proposing would be introduced by whichever government were elected at a subsequent General Election.

One can see why, as a political party and a government, Mr Salmond and his supporters need to set out their plans. And I can see why they want to suggest a Yes vote would offer these policies, because their primary distinction is that they are not in place elsewhere in the UK.

But an SNP government is not independence; in fact, one of the likeliest consequences of independence would be the break-up or radical transformation of the party. The main reason most Scots, even when they approve of them, distinguish between the SNP Government and its policies and a vote for independence is that the former needn't be forever.