It was difficult to be a Scot in London yesterday, because for once it felt like the real action was elsewhere. Alex Salmond's speech to the Scottish Parliament in Edinburgh, in which he laid out the details of the SNP's constitutional position and plans felt like some kind of historic moment.

It was either the beginning of the end for the telos of Scottish Nationalism, of complete independence, or with the referendum scheduled for Autumn of 2014, perhaps it is better viewed as the end of the beginning.

The speech had many interesting moments, but I want to focus on Salmond's curious position on the so called third option of 'devolution max' or 'independence lite' which appears to be what the Scottish people currently want i.e. fiscal autonomy within the United Kingdom.

On this matter he appears to be saying that if it was up to him, there would just be a single clear question: 'Do you agree that Scotland should be an independent country?' Leaving aside the fact that the wording is extremely leading, and will never be accepted by the other side, his position is that while he wants only this question, 'democracy' suggests there should be a third option of devolution max. Sounds like political strategy to me.

The way we structure choices directly effects outcomes. Cameron and Salmond know this, which is why the details of the referendum are so crucial, and why the power struggle to determine them now are not just a rehearsal for the battle ahead, but the first and most important stage of it.

The problem for Salmond's opponents is that there is no safe position to take with respect to the third option, and it would be more convenient for them if the option was not part of the discussion at all. This must be part of the reason why Salmond prefers to keep the option open for as long as possible- because it is a toxic issue for the other side.

Professor John Curtis recently suggested it is risky to deny Scots the third option because it may antagonise Scottish voters and make them more inclined to vote for full independence, and I have spoken to Scottish friends who share that view. However, I would suggest it is even riskier for Unionists to allow it.

Personal Perspective:

Before explaining why, I should say that my equivocal attitude to independence appears to be fairly typical of the people who will be asked to vote in the referendum. We now know ex-pats won't have a say in the referendum, but, bizarre though it sounds, I can hypothetically imagine myself voting for the status quo if there were only two options, and for full independence if there were three.

I write as a relatively anglicised Scot who has spent most of my adult life in England. If anything this experience has heightened my sense of being Scottish, as has representing Scotland internationally for years as a chess Grandmaster, where I have resisted attempts to collapse our national teams into one British team, dominated by England, and annoyed organisers by insisting that English players be represented by the St George's flag rather than the Union Jack.

Like many others, I am excited by the idea of independence and can imagine a flourishing nation state that is more truly a social democracy. But my attitude is almost flirtatious. Creating a new state for an old nation feels like a thrilling adventure, a great story to be told, but I am less sure it is an expression of collective identity or a cool judgment about our national welfare. I am curious, giddy even, to see it happen, but it also feels indulgent and unnecessary.

I identify with the unique geopolitical set-up that is the UK and I am wary of what cessation might feel like in practice. There is something precious about our geo-political structures having evolved through historical osmosis rather than being rationally designed at a single moment. A split would be more like the velvet divorce in Czechoslovakia than the bloody partition of India and Pakistan, but I can still imagine waking up afterwards and thinking: Did we really have to do that? And when foreigners ask, as they often do: Is Scotland part of the UK, or is it a separate country? I like the fact that both is the right answer.

It is not just that I am British and Scottish, but rather than what it means to me to be British is to be Scottish. It is to be a distinctive part of a mutually rewarding partnership, without any fear of fusion.

While the most recent poll suggests growing(but by no means galloping) support for independence, the fact that people like me have views that are fluid and suggestible is why the third option will be pivotal. As well as my personal interest, I view the referendum from the perspective of behavioural economics, which informs my day job directing the Social Brain Project for the RSA.

Choice Architecture:

The big point here is that the Scottish electorate have never before been asked to directly compare 'devolution max' with full independence, and the salience of that comparison will shape preferences in the months ahead in a way they haven't had a chance to before. Pollsters don't seem to have grasped this point, but I suspect SNP strategists have.

Simply stated, we are not nearly as rational as we like to think, and our voting patterns are easily manipulated. I suspect most Scots feel fairly ambivalent about their constitutional future. Having heard the case for and against independence for years, their vote will depend less on rational persuasion leading them to a settled position, and more on a variety of cognitive biases that will lead them to vote according to the way the options are worded and framed.

For instance status quo bias means we tend to weigh the costs of the change more heavily than the gains, especially if the nature of the change is complex or uncertain. Similarly, the endowment effect tells us we often over-value what we have simply because we have it, in this case the Union. If you compare independence only to the status quo, many will opt for our current arrangement simply because of uncertainty over details of the change(which currency? how much debt? what kind of defence? relationship with EU?) and the no-campaign are certain to maximise the degree of uncertainty and play off it. They won't use this language, but they will make you think of the tangible things you will lose compared to the intangible things you will gain.

However, the point is not that we are risk averse, but that we think in a relative way. Nobody has a view of independence in itself, but only relative to their perception of how the current system is working, and how the other options sound. As Voltaire put it in response to the comment that life is hard, "Compared to what?"

To explain why the third option matters, consider an analogy outlined by Dan Ariely. When participants in a study are offered a choice between an internet only magazine subscription for £40, a print only subscription for £80, and a print and web subscription £80, the vast majority go for the third option, largely because it is viewed favourably compared to the second option. So far so obvious, but when you remove the second option that nobody goes for, you would assume people would make the same choices. In fact, the majority then opt for the first option, internet only, which now compares favourably relative to the remaining option.

In this case, the middle option functions as a decoy, and was obviously bad, forcing people to make a different kind of relative judgement. In most cases we actually show a bias for the middle option, simply because the in-between option feels like it is more likely to be the right answer. In this case, that would mean devolution-max for Scotland, which 68% have said they would vote for, according to Ipsos Mori, but the point about comparisons remains. In either case what matters is the choice architecture- not so much what the options are, but how they stack up against each other. We make decisions by comparing things, and we compare whatever is most comparable.

By inserting the option of devolution-max, you do not merely add a third choice, but also create a reference point for the other two options. Devolution-max is easily compared to full independence, because it would lead to a similar domestic outcome, and it can be easily compared to the status quo because the Union would remain intact.

The critical question, that has not yet ever had a chance to play out in public, is how voters view full independence relative to devolution-max. When you grasp the importance of relative thinking, it becomes clear that to those who are in favour of devolution-max, full independence might start to look like a weaker version of what they really want. In relative terms, if we are willing to go that far, some may think, what's stopping us going all the way?

Rather than just being one of three possibilities, devolution-max will become the touchstone of the argument for most Scots, shifting the conversation away from the current dialectic of 'separatism' v 'unionism' or 'courage v prudence'.

Our tendency to make comparative judgements suggests that including the third option all but guarantees some extension of Scottish powers. This is most likely to happen because Scots will opt for the middle option of devolution-max, but it is also possible that full independence might start to look more attractive relative to the compromise option.

When the Scottish people compare the status quo with independence, independence looks risky, but when they compare independence to devolution max, it may begin to look like a truer version of the autonomy they already desire.

A great deal will depend on the details and the wording of the referendum, but in general the choice between full independence and the status quo loads the dice in favour of the current arrangement due to our bias against change, while the third option of devolution-max might actually make full independence more likely due to our tendency to make comparative judgements.

I think Salmond is very aware of the importance of comparative thinking, which is perhaps the real reason why he wants Scotland's constitutional conversation to go on for 1000 days.