Glenn Campbell: Nicola Sturgeon's caution over second referendum
The SNP went into the last Holyrood election with a clear commitment to hold an independence referendum.
They said it would take place in the second half of the parliamentary term and it did on 18 September 2014.
Party leaders used to describe this as a "once in a generation" or even a "once in a lifetime" event. They no longer do.
They reserve the right to ask the independence question again much sooner than that.
As the referendum anniversary approaches, Nicola Sturgeon is promising to set out in her 2016 Holyrood manifesto "the circumstances and the timescale" for a re-run.
But don't expect the sort of unequivocal commitment the SNP gave in 2011.
Instead, expect scenarios that could trigger a ballot, such as a UK vote to leave the EU in which Scotland has voted to stay in.
In any event, Ms Sturgeon does not want to hold another referendum unless she is sure of winning.
That means that opinion polls would need to be consistently suggesting majority support for independence.
Ms Sturgeon thinks this is more likely to happen if the new Labour leader Jeremy Corbyn is unable to establish himself as a prime minister in waiting.
If Labour don't appear to have a credible chance of winning the next general election, the SNP leader said "many more people in Scotland are likely to conclude that independence is the only alternative to continued Tory government".
It is perhaps that kind of thinking that led the former boss of the Yes Scotland campaign for independence, Blair Jenkins, to suggest a second referendum in 2021.
By then we'd know the outcome of the next UK general election and the SNP would be able to seek a mandate for a referendum in their 2021 Holyrood manifesto.
Meanwhile, there will be no shortage of suggestions from independence supporters for scenarios that Ms Sturgeon should say could trigger an earlier vote.
For example, her predecessor as SNP leader and first minister, Alex Salmond, has said that renewing the Trident fleet of nuclear armed submarines could be a reason.
That decision is due to be taken at Westminster next year. But, despite opposition from the SNP, Jeremy Corbyn and the Labour MPs who follow his lead, there is still likely to be a large majority for renewal.
In other words, to make Trident a trigger would be to all but promise a second referendum.
Which is precisely why Ms Sturgeon is unlikely to endorse the Salmond plan.
At the risk of repetition, she wants to keep her options open and to hold another vote only when she is confident of victory.