A cynic might say David Cameron has an interest in a strong SNP. After all, a meaningful Tory revival in Scotland seems as far away as ever (though it would be closer if the SNP withered away) and this being so, the Tories have an interest in seeing the nationalists win Labour seats at the next election. In that limited sense then, to vote for the SNP is, in one respect, to express the preference that Cameron, not Gordon Brown be Prime Minister. And, of course, there are plenty of nationalists who think that a Tory victory at Westminster will be Scotland's opportunity. (More on this later). Perhaps. So, a temporary alliance of convenience? Well, only up to a point.
As I say, that's the cynical view of Cameron's comments in Scotland on Thursday. I think there's more to it than that. Campaigning in Fife, Cameron took a commendably broad-minded view of the Union. Of course, he said, an independent Scotland would not immediately or automatically be a basket-case:
"I don't think we'd ever succeed in saving the Union by frightening Scots to say you couldn't possibly make it on your own. That's not the way I approach it. The Union to me is about generosity – we're stronger together because we share so much together."
The contrast with the kind of sneering, boorish Unionism that stresses economics and presumes some kind of crippling inadequacy that renders Scotland unusually incapable of ordering things is a) significant and b) encouraging. I think it probable that you can win the Unionist argument on economic grounds, but doing so demands that you sour Scotland in order to save her. The country is unlikely to be at ease if the constitutional question is settled by scare tactics. The idea that independence isn't feasible is both infantile and, worse, infantilising. It breeds a chippy sense of resentment in a country already more than well-stocked with the stuff.
No, the case for the Union - and it's a perfectly strong one - needs to be made in terms of culture, not economics. It's a question of temperament, of history, of, yes, values and culture and all the other stuff that's bundled together and covered by the Union Flag. Three hundred years is a lot of water under the bridge.
The other importance of the cultural argument for the Union is that it's a positive argument. Something that people can be proud of, not humiliated into supporting because without it we'll be left destitute in the streets, impoverished and even more malnourished than is currently the case. The economic argument comes too close to being a Unionism of charity; the cultural argument rests upon three centuries of a remarkable partnership. Not just a lesser Scotland without England but a lesser England without Scotland. And so on.
I think Cameron appreciates this. If so then that's to his credit. (And perhaps the influence of Michael Gove too?) It shows Cameron to be a bigger politician than is sometimes supposed and one, moroever, with a sense of the bigger and for that matter longer-term questions of Britain, the Union, Britishness and Unionism.
UPDATE: As you might expect, Scottish Unionist has more.