Next week, Alex Salmond, First Minister, will offer for our consideration a white paper on his plans, or hopes, for a constitutional referendum. By most yardsticks, it sounds a curious sort of gambit. It counts as a promise kept, and few will argue with that. But it is also, in both senses, a paper exercise. We will not be voting on independence any time soon.

Salmond, though, has had no difficulty honouring his pledge. How could he do otherwise? The "SNP duck independence issue" headlines would have followed swiftly. Party natives would have grown restive. And the sense that a principle had been traded for power would have been inescapable.

It's an odd affair, nevertheless. The SNP has formed a minority administration for a couple of simple reasons. One has to do with an old political problem: too few friends; or rather, too few Unionist parties prepared to give aid, comfort, or the appearance of aid and comfort, to the enemy. The second reason involves brutal reality: the Nationalists are, indeed, a minority, albeit the biggest we have, and have yet to persuade better than one-third of voters to support them.

Salmond is more relaxed about all of this than might have been predicted. Why punt a white paper preparing the way (you hope) for a referendum you cannot (as you well know) hope to win? Who seeks defeat, promise or no promise? Clearly, this is not the First Minister's cheery view of the world.

The white paper, he tells us, is intended only to launch "a national conversation". This is not Devolution II: the Final Showdown, or anything like it. Who is so churlish as to refuse a chat? More to the point, who is so lacking in the courage of their Unionist convictions as to refuse a friendly debate? Eck the Knife has a friendly grin, and teeth, as the song said, like razors.

The white paper still sounds like a waste of time, for all that, especially if you take (with tongs and rubber gloves) the Scottish Daily Mail. Yesterday, that newspaper was trumpeting glad tidings. "Scots reject independence" its front page said in big, extra-bold serif. As ever with the Forgers' Gazette, this wasn't quite the truth, not unless 31% of Scots had been disenfranchised.

What the paper meant to say was that support for independence had fallen from a historic high of 51% in a January poll to 31%, close to the historical norm. The point was well-made, nevertheless. Salmond's well-reviewed and sometimes ingenious leadership during his first 100 days has given his party a thumping lead over Labour. Since the elections, the latter has stuck fast on 32%. The Nationalists have climbed from 33% to 48%. Yet support for independence has shrivelled. What's gone wrong, or is it right?

Progressive Scottish Opinion questioned 1012 adults across the country during the first week of August. Unless there was something very strange about the methodology - and I have no reason to think so - that's a robust, more-than-adequate sample. It cannot be easily rebutted, either, by an otherwise delighted SNP claiming that responses towards independence depend on how you ask the question. The Mail said it asked only whether members of its sample approve or disapprove "of Scotland becoming independent". Clear enough, surely?

Voters are fickle: you don't need a poll to prove it. If the election result was anything to go by, even allowing for the complexities of the voting system and a fiasco on the day, large numbers of January's 51% had thought again before May, far less before August. It may be that a majority do not want, and will never want, what the Mail terms separatism. Yet it could also be that we are witnessing one of the larger ironies of recent times.

Is the evident success of a Nationalist administration stifling support for independence? Do voters want no more from their government than energy, competence and a willingness - second nature to Salmond - to speak for Scotland? But isn't that just devolution working, finally, as devolution was supposed to work? And is Salmond content with that? Some people on his own side, nominally at least, fear that he is.

I disagree. First, there is the fact of minority government. It can't be wished away. As we have seen in the broadcasting debate, Salmond's administration may style itself a government, but it is forced to operate as a mandated pressure group. The same will be true, in spades, when the talk turns to oil and gas revenues, or to any attempt to seek more power for Holyrood. Salmond can insist, cajole or beseech, but he will only succeed if he persuades. He knows it, too. He also knows that there is more than one way to skin a constitution. His real task is somehow to make public perceptions of the Scottish interest and of independence cohere. Running a minority administration, he must therefore explore an important distinction made by the great Tom Nairn.

You can have de jure independence, as Tom called it, the old tear-up-the-treaty, seat-at-the-UN variety, if a majority can ever be persuaded to take that step. But you can also have de facto independence, with power repatriated steadily, bit by bit, to Edinburgh, and leave aside the formalities. That kind may, in fact, reflect the realities of the modern world. It won't scare too many horses, either. Salmond, I'm convinced, wants the de jure variety still, but he'll settle for the de facto sort if he must. Given his situation, his best bet is to view the latter as a route to the former. That certainly renders him a gradualist, as some have sneered, but he is a gradualist in a hurry. The more arguments there are about Scotland's place within the United Kingdom, whether in broadcasting or defence policy, the better.

Still, the fact that support for independence has yet again fallen away (the Mail's poll replicates previous findings down the years) should trouble the First Minister. The approval ratings for his executive are better than excellent. Gordon Brown's arrival in Downing Street has done nothing whatever for Labour (the Prime Minister should also be troubled). But if voters have taken to the SNP to such an extent, why do 69% still refuse what the SNP is selling?

Salmond, I think, must calculate in the following manner. He lacks support for the Nationalist end-game, but there are any number of moves on the board of which that 48% would, conceivably, approve. In that sense the white paper will be part of a national conversation, if such language is to your taste, but it will also count as part of a larger propaganda exercise. Trust and reliability are, as ever, key words for the SNP. They represent honourable ends in themselves, but they are not the only ends in view.

None of which means that Salmond would be delighted to hold a referendum tomorrow. He would deny that, of course, just as he would deny that minority government would have been his first choice. He has turned the problem to his advantage. Now he must turn his advantage into an instrument of persuasion.