Twenty years ago, as the old Soviet Union crumbled, Russians suddenly realised they didn't know where "abroad" was anymore.
Was Ukraine now "foreign", despite centuries of shared history? And if not, what was it?
Andrei Kozyrev, Russia's then foreign minister, came up with an answer. The former Soviet republics, he said, were "near abroad". The expression - like its sister "far abroad" - has stuck.
So Russians dealt with the break-up of their empire by re-imagining the very concept of "foreign". If the UK unravels just like the multi-national USSR, will the British do the same?
Alistair Darling thinks not. In fact, the leader of the pro-union Better Together believes the English, Welsh and Northern Irish would become foreigners "effectively and overnight" on a Scottish independence day. Why? Because rump Britain - whatever it was called - would be a different state. And its citizens, therefore, foreign.
This vexes nationalists. They point out that - almost a century after independence - Ireland is still not, technically, a foreign country. Its nationals enjoy the same rights as British citizens - and vice versa. The two states, the UK and Ireland, share a passport-free common travel area and had a single labour market long before they both joined the EU.
But those are legal niceties. The question that really interests me is whether the Irish think of people from the UK as foreigners.
"I think the feelings that Irish, Scots and Brits more generally have about one another are quite ambivalent," says Piaras Mac Éinrí, an academic from Cork.
"We don't regard one another, in spite of all of the historical complexities (or maybe because of them) as being really 'foreign'."
"The Common Travel Area represents a practical and historical recognition of an obvious fact - that British and Irish lives continue to be closely entwined, notably in the labour market.
"Soccer is a big link too - Irish fans support both English and Scottish clubs.
"Moreover, while the British don't generally get our television very much, all parts of Ireland watch a lot of UK television (although not Scottish).
"It goes well beyond a common language - Irish people seem to be everywhere in the UK media these days, and many of my colleagues are British."
Mac Éinrí is an expert in migration. He's fascinated by the fact that Britons who move to the republic aren't really considered to be foreign immigrants. RTÉ, for example, cheerfully declared Italians to be Ireland's biggest migrant group, forgetting the far bigger contingent of British (now outnumbered, Mac Éinrí points out, by Poles).
Ireland, of course, has been exposed to foreign-language-speakers like never before with mass migration in the last decade or so. But it has never fretted much about British settlers with their shared language and broad cultural terms of reference. 'When we talk about 'the new Irish'," wrote Irish Times journalist Shane Hegarty, "there's a clear sense that we're not including the Brits in that mix."
Scots and Irish intermingled for at least a thousand years before anybody even thought of the idea of Great Britain or the UK.
But the relationship between the two nations, says, Mac Éinrí, is "more nuanced" that than between Ireland and wider Britain.
"There is a tendency to see the Scots as cousins even more than neighbours, with affinities in areas like music," he said. "On the other hand, people with long memories sometimes have an unfavourable view, rightly or wrongly, or the actions of particular Scottish regiments at different times in Ireland, including the south going back before independence."
Darling's concept of "foreigner" - the big F word of the independence campaign - is straight-forward and logical. You are either, after all, British or not.
Me? I think that there are many places - Ireland among them - where the concept of "foreign" comes with a sliding scale rather than a simple binary yes/no switch.
Would the post-UK space be such a place? The omens are, I think, that it would. A poll by Ipsos Mori earlier this year asked the English if they would see Scots as foreigners after independence? The result: two-thirds said they would still feel a common bond with Scots if we vote Yes next year. That, at least, is the view from Scotland's "near abroad". What do you think?
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