As the Scottish independence referendum campaign enters its final stages, both sides will still be hoping that they can persuade as many voters as possible that their side is right. Although undoubtedly some voters are still to decide which way they will vote, the minds of most voters were made up long ago and the campaign will have made little difference. Political psychologists have convincingly shown that voters aren’t particularly good at making objective assessments of arguments about political issues – regardless of their actual validity, we tend to think that arguments that support our positions are good and arguments that don’t are bad. Even when voters have the same factual information, partisan bias leads to very different conclusions. The stability of the referendum polls despite the long and intense campaign suggests that these factors are almost certainly playing an important role in opinions on the independence debate. If vote intentions in the referendum aren’t a result of objective evaluations of the pros and cons of Scottish independence, where do these opinions come from? Political attitudes are not simply created in a vacuum, nor do they just reflect self-interest according to socio-economic position. Scholars have long suspected that political attitudes arise from deep-seated psychological dispositions – particularly from differences in personality. For psychologists, ‘personality’ captures the patterns of thought, feeling, and behaviour that are relatively stable within individuals in different situations and across time: people who are organised at work are also likely to be organised at home; shy children often grow up to be shy adults. For the past few decades, the leading paradigm in personality psychology has been the ‘Big Five’ approach, which has shown that much of the variation in personality traits between people can be captured by five dimensions – agreeableness, conscientiousness, emotional stability (sometimes labelled ‘neuroticism’), extraversion, and openness to experience.

Martin Wolf is quite right when he says that the debate about Scottish independence should not focus on relatively short term macroeconomic costs and benefits. I personally would be very sad if Scotland became independent, but that has nothing to do with money and (just as for Martin) everything to do with a British identity of which Scotland is an important part. But I also understand, having lived and worked in Scotland for five years, how these issues are more difficult when you are a minority part of a bigger nation. Nevertheless my expertise is in macroeconomics, so I should say something about recent claims by both sides. It seems fairly clear to me that the Treasury report is right when it argues that, for the next decade or so at least, people in Scotland will be significantly better off by staying in the Union. The main reason is that additional public spending in Scotland as part of the union exceeds any benefits Scotland would get from having more of the revenue from the North Sea. This is also the conclusion of independent bodies like the IFS or NIESR, and it is only avoided by the Scottish government because they have unusually optimistic projections, particularly for North Sea revenues.

For quite understandable reasons, much of the debate about independence for Scotland has so far focused on the economic consequences of seceding from the UK. This, after all, is what most political argument inside liberal democracies is about – small economic gains and losses that might accrue to different sections of the population. For politicians brought up in this culture, it is not surprising that they should appeal to voters in the referendum on that basis: will they be £500 pa better off or £1,000 pa worse off if Scotland becomes independent? But should this really be the focus when what is at stake is a fundamental redrawing of the boundaries of a democratic state, and the ending of at least three centuries of political co-habitation in a single unit? Admittedly Alex Salmond does intersperse his economic arguments with appeals to democratic principle. He objects to Scots being ruled by a Westminster government that they did not elect. But the trouble with this argument is that it can be reiterated endlessly wherever the political boundaries are drawn. In an independent Scotland governed by the SNP, Labour voters in Glasgow or Liberal Democrats in the Shetlands could make exactly the same complaint. Should we conclude that these places should withdraw from Scotland and become mini-states on their own?

In July 2014, Jean-Claude Juncker was designated as new President of the European Commission. It may be that he will take a more neutral approach to the question of an independent Scotland’s EU membership than that of his predecessor, José Manuel Barroso, who famously stated that it would be: ‘extremely difficult, if not impossible’for an independent Scotland to join the European Union. The puzzle is why Barroso (and some other EU officials) should appear negative about the prospect of an independent Scotland’s continued EU membership. For while either side of the independence debate may have a strong interest in portraying Scotland’s future in the EU as either plain sailing, or as a via dolorosa, the EU itself should have no such vested interest. I write ‘should’, for in the EU, as in other areas of public life, the fractional and the partisan of politics all too often dominate over matters of principle.

When the Scottish government released its White Paper outlining what an independent Scotland might look like, migration policy was a small but essential element of it. The White Paper promises a change in the direction of travel in migration policy for an independent Scotland. In recent years the UK has enacted a number of measures restricting various migration flows, and the present government aims to reduce net migration – the difference between immigration and emigration – below 100,000 annually. The White Paper outlines a vision for a set of migration policies that encourage skilled migrants to come to and remain in Scotland, in order to meet different demographic and economic objectives, which it explicitly contrasts with the present ‘Westminster approach’.

Much of the discussion around the relevance of migration and migrants to the Scottish independence debate revolves around the effects of independence on current immigration policies in Scotland and the rest of the UK. But in the last two centuries, Scotland’s population change has been characterised more by emigration than by immigration. Clear data on the actual size of the Scottish diaspora are hard to come by and are critically dependent on how one chooses to define ‘Scottish diaspora’. The number of people born in Scotland and living outside the UK, for example, is estimated at about 200,000, while about 850,000 Scottish-born people are believed to live elsewhere in the UK (Shaw 2013). These relatively modest numbers are dwarfed, though, by estimates of the size of the ‘Scottish diaspora’ using looser interpretations of the term that include those with more distant Scottish ancestry, in particular those who still consider themselves to be, in some way, Scottish. When these more distant ‘Scots’ are included, estimates of the size of the diaspora increase to more than 30 million (Sim 2011) – with some suggesting the number could be as high as 100 million. Clearly, larger numbers relate to those whose sense of Scottishness is based on more distant heritage – potentially going back several generations – or even less tangible relationships with Scotland.

There are a number of important arguments for why Scotland should remain part of the United Kingdom: the need to avoid further economic turbulence in already troubled times; the benefits of being a relatively large country with far-reaching international influence; and the long history and common values that we share with the Scots. But perhaps most important of all is what I shall call the Union Jack argument: the prospect that we might have to relinquish what is, by any objective standard, the best national flag in the world. For readers unfortunate enough not to be familiar with the Union Jack, it comprises three main elements: a red St George’s cross overlain on a white background, which represents the nation of England (and Wales); a white St Andrew’s cross overlain on blue background, which represents the nation of Scotland; and a red St Patrick’s cross overlain on a white background, which represents the nation of Northern Ireland. The flag first took its present form on the 1st of January 1801 when the Kingdom of Ireland and the Kingdom of Great Britain were brought together under the Acts of Union 1800.

Should Scots vote for independence, this will be the first case of secession from an EU member state. There is no precedent which would suggest whether or not an independent Scotland would (automatically) become an EU member state and whether Scots would retain rights stemming from EU citizenship. Analogies have been attempted with Algeria and Greenland, but they crucially differ from Scotland in law and fact. Algeria was effectively a French colony, although formally a Department, and its independence was a matter of decolonisation. This is not the case in Scotland. Greenland remained under Denmark’s authority, but exited what was then the European Economic Community (EEC). Scotland is seeking to do the opposite – leave an EU member state and remain in the EU. The EU is based on international treaties. When new states emerge, some treaties indeed continue to apply in the territory of the new state, if the predecessor state was a party to them. The treaties regulating human rights and humanitarian matters are particularly known to operate in this way. However, there is no such automaticity where treaties that establish international organisations are concerned. Strictly speaking, the EU is not an international organisation, but such an analogy can be established for our purposes here. The UN Charter is also a treaty and an independent Scotland would not accede to it automatically, either. It would need to apply and become a member anew. The same would happen with its EU membership. By becoming independent, Scotland prima facie also exits the EU. However, there is a structural problem in EU law about such an exit.