Momentum in politics is a potent force.

A campaign boosted by a few weeks of positive headlines can soon build a head of steam that is enough in itself to draw in new supporters.

Yes Scotland has benefited from momentum during the winter, seeing its poll ratings rise, and Alex Salmond hopes with his speech today to keep that going.

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His words will be directed over the heads of the party faithful at the SNP conference in Aberdeen towards those in the wider public who are yet to make up their minds, and his strategy is simple: to try to convince them that independence is inevitable. Dispensing with the conditional tense as if the referendum were bound to go only one way, he will state that negotiations "will" begin with Westminster before the end of September. A so-called Team Scotland negotiating group "will" be convened. And on 24 March 2016, Scotland "will" become an independent country.

Activists meeting in Aberdeen to share campaigning ideas and inspire one another to keep up the good work do not need much convincing. There was yesterday a palpable sense of confidence in the main hall, in fringe meetings and in conversations in the cafes of the Aberdeen Exhibition and Conference Centre. For the No campaign, this bullishness will be a real worry. They have watched Yes Scotland hold possession and play the ball up the field while seemingly transfixed, their warnings over the economics of independence having failed to translate into a poll boost.

To stay in the game, they must find a way of seizing the initiative back and focusing on the positives of staying in the UK.

Mr Salmond's speech will be big on the positives of independence, but in private, he is likely to be concerned by signs that, having gained a few polling points during the winter, the growth in popularity for independence may have stalled. The high priest of polling, Professor John Curtice, points to indications this week of opinion stabilising, with No still clearly ahead.

Mr Salmond's other big message in his speech will be that the referendum is not about the SNP, nor about himself as First Minister. This is also, perhaps, a response to polling, which shows that Mr Salmond is Marmite to voters: some love him, while some, it must be said, do not. His aim now is not to waste time preaching to the converted, but to woo those sceptics.

The deputy first minister Nicola Sturgeon in her speech also sought to reach out past party lines, calling on Labour supporters to back independence in order to "reclaim" their party, but hers was essentially an rallying cry to the faithful.

There must have been times since last summer when SNP supporters feared their last conference before the referendum could be a troubled affair; its bullish, cheerful atmosphere will buoy them up. Right now, Yes Scotland has the happier story to tell. The Yes camp have taken much encouragement from their poll increases, but would be foolish to underestimate the resolve and passion of those who wish Scotland to remain in the UK. In spite of suggestions to the contrary, the referendum result is not yet decided - nowhere near.