EVER since Nicola Sturgeon became SNP leader she’s been asked if her party’s manifesto will include a commitment to hold another independence referendum. In general terms she’s played this down. Last year’s general election manifesto contained no such pledge, indeed it said that independence was “not what this election is about”. Nor, it might be added, this one.

Earlier this year there was even speculation it wouldn’t include specific proposals to hold another referendum at all, the first since 1999 not to do so. “News to me,” Ms Sturgeon tweeted in response. “Manifesto not finalised yet.”

Well, it’s finalised now, for the SNP’s pitch for a third-term government will be unveiled in Edinburgh on Wednesday, and yesterday the First Minister confirmed a second referendum would only take place if a) “there is clear and sustained evidence that independence has become the preferred option of a majority of the Scottish people” or b) “if there is a significant and material change in the circumstances that prevailed in 2014”, such as Brexit.

Rather than representing a major break with previous SNP manifestos, this actually continues a tradition of keeping referendum talk as vague as possible. Most manifestos since 2001 have referred to an independence plebiscite only in general terms, while even the 2011 Holyrood prospectus merely pledged to “bring forward…proposals to give Scots a vote on full economic powers”. There was no accompanying timescale.

So it seems Wednesday’s document will neither rule out another referendum nor rule it in, which allows the SNP to keep its options open. Otherwise this election resembles a retread of 2011’s “team, record, vision” campaign, although paradoxically the last of those still needs the most work – while the first referendum normalised the independence proposition, it also acted to highlight its weaknesses.

The language used to date merely acts as a guide to the approach that won’t be taken. Earlier this year the First Minister spoke of making the case for independence “in a realistic and relevant way”, while at the SNP’s spring conference she said the party should be prepared to challenge some of the “answers” deployed in September 2014. There would be no attempt to browbeat anyone, she added, rather the SNP would seek to change Unionist minds “patiently and respectfully”, a none-too-subtle repudiation of her predecessor’s often heavy-handed approach.

At the spring conference the First Minister also announced a summer initiative to rebuild the case for independence, and re-watching that part of her speech her reaction to the audience’s response (a sustained standing ovation) is interesting: Ms Sturgeon doesn’t smile or acknowledge the obvious enthusiasm, but rather tries to carry on with her speech. She obviously didn’t expect the word initiative to provoke such an enthusiastic response.

Now what form this (National Conversation Mark II, as one former aide called it) takes remains to be seen, but the trouble Ms Sturgeon has in rejuvenating the case for independence is that her predecessor’s arguments continue to cast a giant shadow. Salmond spent decades recasting independence as primarily an economic project, or more crudely a means by which Scotland could jettison low economic growth and Tory “austerity”.

For obvious reasons, that presently leaves the independence project in a difficult place: even if the oil price bounces back it’ll lack its previous potency, while the GERS – Government Expenditure and Revenue Scotland – figures speak for themselves. As the gamekeeper-turned-poacher Alex Bell put it a few months ago, the SNP’s mistake was not to advocate independence, but to have promised wealth, too.

In a recent interview Ms Sturgeon attempted to distance herself from that aspect of the 2012-14 independence pitch, protesting that she’d never gone into a public meeting and claimed an independent Scotland would be a land of milk and honey. She accepted, however, that the “overall presentation maybe appeared more like that”, partly as a response to what she called the “hell in a handcart, the sky will fall in, we’ll be paupers” argument of Better Together.

Some of the smarter SNP MPs at Westminster are also conscious of the need to move the independence case from oil or renewable energy-based arguments, although identifying a compelling alternative is still in the early stages (as I’ve observed before, fracking could’ve been an option had the party not cast it as “Unionist” and therefore bad).

At least a couple of Nationalist MPs have been reading a book called The Industries of the Future by the Hillary Clinton adviser Alec Ross. This accepts that the nature of innovation will soon evolve even more quickly than it has since the mid-1990s, pointing to fields like robotics, artificial intelligence and the impact of digital technology as those most likely to shape developed countries’ economic futures over the next decade. Perhaps the bookworm First Minister is aware of it, too, for yesterday she said a renewed independence case would “be relevant to the complex world we live in today”.

Alex Salmond’s language has been revealing in a different way. A few weeks ago he said the independence argument needed refurbishment, term that implied a cosmetic change rather than anything deeper. For example, he restated his belief in the retention of sterling, but said a better case was necessary to prevent being “gazumped” by opponents in a future referendum.

Logically, this hints at a policy of “sterlingisation”, something floated by Salmond during the first referendum but not in a particularly coherent way. Nationalist thinkers, however, are acutely aware that currency was central to failure in September 2014 and therefore central to future success. Expect more detailed work on this during the next Holyrood session.

The SNP also needs to develop a less opportunistic independence proposition, one that doesn’t depend upon Tory government at Westminster, austerity economics or illegal wars for potency, but something that stands alone: principled, deeply-thought through and creative.

Critical voices saying that the SNP version of independence is too conservative, meanwhile, are on the rise, while Professor John Curtice has suggested (unhelpfully from the SNP’s point of view) that the best way for voters to maximise the number of pro-independence MSPs in this election is to use the regional list vote to support RISE or the Scottish Greens. An SNP spokesperson gave this short shrift, melodramatically suggested that such a course risked “playing into the hands of those who oppose a fully self-governing Scotland”.

The forthcoming election, therefore, represents a twin threat to the SNP’s ownership of the independence issue. If the Greens and RISE do well then it’ll find itself pulled in ideological directions it believes are electorally unhelpful, while another overall majority might discourage a more thorough reboot: if the SNP keeps doing so well on the basis of superficial debating points, it risks convincing itself that one more heave, one more referendum, will be enough.

That would be a mistake. The party doesn’t just need to equip itself with “different” arguments ahead of indyref2, but better ones: more realistic, more original, less sanctimonious. It’s a tall order, but time and money – at least at the moment – is on the SNP’s side.