Chris Mason: The two huge tasks of persuasion for the SNP

"We are the independence generation."

So said the SNP leader and Scotland's First Minister Nicola Sturgeon as she closed her party's conference in Aberdeen.

Like all of these political gatherings at this time of year, they are an assembly of the convinced who have to persuade those who are not.

But for Nicola Sturgeon and the SNP, there are two tasks of persuasion - and they are both huge.

The first is to make the case, via whatever means, for another independence referendum.

And the second is to win it.

Clearly the second isn't possible without the first, and securing the first is proving very difficult.

Many would agree that the SNP has a powerful argument, grounded in democracy, for another vote, given a majority of members of the Scottish Parliament want one.

But the power to grant a referendum is, to use the jargon, reserved, which means it lies with Parliament in Westminster, not the one in Holyrood.

And Westminster says no, saying the last referendum, in 2014, was a once-in-a-generation event, just eight years ago.

Hence the case beginning this week at the Supreme Court in London to determine whether the Scottish Parliament can pass a law for an advisory referendum without the consent of the UK government.

The weight of legal opinion suggests the Scottish government will lose that case, and so Nicola Sturgeon will be left with her Plan C.

Plan A was Westminster saying yes to a referendum. It hasn't.

Plan B is the court saying yes. It probably won't.

Plan C is turning the next general election into a referendum, even though it, well, isn't one.

The SNP argue that if they won more than half the votes in Scotland in a general election that would do the same job as a referendum and count as a mandate to leave the UK.

The party would be setting itself a mighty high bar, for an election they would call a referendum, but no one else would.

To give you a sense of just how high a bar it is, they could win every seat in Scotland and still fall short.

If they won, the government in London could still say no.

And if they lost, that would probably spell the end of Nicola Sturgeon's leadership of her party and of Scotland.

Not that there was any sense of such defeatism in the air in Aberdeen.

Perhaps the biggest cheer of her entire speech came when she said she intends to remain Scotland's First Minister for "quite some time yet."

Ms Sturgeon is the most experienced political leader in the UK, leading the most consistently electorally successful party in the UK of recent years. But they didn't win the only electoral contest that really mattered to the SNP: the last independence referendum, which they lost.

For a party that has been in government in Scotland for 15 years, they continue to defy gravity: despite strong criticisms of their record on the NHS and schools, the highest rate of death from drugs in Europe and ferry orders that are late and over budget, they keep doing miles better in elections than anyone else in Scottish politics.

They hope, particularly if they keep winning, that democratic justice eventually must prevail, and they will get another referendum.

But that is far from certain, and even if they do, the mighty task of winning one then begins.

Senior figures now acknowledge privately that in 2014 they didn't have adequate answers for the big questions: what would Scotland's currency be, in the short and long term, after independence?

How would the border work between Scotland and England?

How soon might Scotland re-join the European Union, and with what consequence for both currency and the border?

Two big questions, of many big questions.

And answers required, as Nicola Sturgeon acknowledged in her speech. "I know that what gives many people most pause for thought on independence is the economy," she said.

But in the short term, it's back to that court case, and the next election.

A next election where Labour - as things stand now at least - look like they could win, so robbing the SNP of their bogeyman of choice, the Conservatives.

Already we see the party shifting its focus towards Labour to acknowledge that, with the SNP's Westminster leader Ian Blackford getting a laugh during his speech the other day.

He said: "I'm afraid I can only think of one sentence more ridiculous than the Tory's 'Get Brexit Done'. And that's Labour's new slogan - 'Make Brexit Work. Never before have so few words made so little sense."'

The prospect of a Labour government at Westminster will spook far fewer voters in Scotland than a Conservative one, and may tempt rather more to vote for them than have done recently, although SNP officials take comfort from polls that suggest Labour is taking votes from the Tories rather than from them.

The SNP is a party that has been in power in Scotland for 15 years, with a leader who towers above her political rivals in Edinburgh.

The party remains the overwhelmingly dominant force in Scottish politics, and yet the prize they really cherish, independence, and the route to getting it, a referendum, remains elusive.

For now, in government, they continue to mould a nation, Scotland.

But they still dream of more than remoulding the United Kingdom, but recasting it permanently, with Scotland's departure.

Achieving that still seems some way off.