It was the historian Arnold Toynbee who referred to the "dogma" that history is simply "one damned thing after another".

And so, if boiled down to its essentials, it is. Last weekend I watched Rona Munro's engaging journey through one damned Scottish thing after another in her 15th-century trio of "James Plays".

As she explained elsewhere, at a point when Scotland is deciding its future few things can be more useful than taking a look into its past, and indeed the three plays chart the ebb and flow of Anglo-Scottish relations.

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James I was England's prisoner and sent home with an English bride, later emerging as a strong and independent ruler; James II went to war with England; and James III fluctuated between courting English favour and reaching out to France. All of them, however, lived in the shadow of their larger, wealthier southern neighbour.

This central truth emerges from all three plays, perhaps betraying the playwright's position on the million-dollar question. In the programme notes, however, Munro coyly admits her plays "contain a statement, but not necessarily a clear one".

Such ambiguity is useful for any cultural exploration of a complex debate (a point missed by more strident referendum-themed theatre at the Fringe), although yesterday Sir Tom Devine - by common consent Scotland's leading historian - threw caution to the wind and declared for Yes, having previously joked that the present and future were not his period.

Obviously Sir Tom is entitled to take a position, although parts of his supporting argument are curiously vague and contradictory for such a rigorous academic. Key to his "long journey" from ardent No to confirmed Yes has been the development of a "more confident political and cultural landscape", to which he himself has contributed through historical research.

In this Devine finds himself in agreement with the First Minister, and indeed the two men explored this theme during their convivial appearance at the Edinburgh International Book Festival exactly a week ago. At the same time, however, the historian buys into less convincing aspects of the pro-independence case.

One of these, the view that Scots are wedded to a "social democratic agenda" unlike England, which, since the 1980s (Sir Tom's timescale rather than mine), has "embarked on a separate journey" is astonishingly reductive. Two complex and varied nations are thus boiled down to "left-wing Scotland" versus "Tory England", when by any measurement both countries contain multitudes.

Paradoxically, Sir Tom then approvingly cites the "silent transformation" of the Scottish economy away from heavy industry towards a "more diversified model" based on light manufacturing, financial services and the public sector, a line that regularly featured in Margaret Thatcher's Scottish speeches. So within a few paragraphs the historian both disapproves and approves of a major (not to mention painful) political and economic shift associated with the 1980s.

Sir Tom's central point, however, is a historical one. "The union of England and Scotland was not a marriage based on love," he argues (or rather asserts). "It was a marriage of convenience. It was pragmatic. From the 1750s down to the 1980s there was stability in the relationship. Now, all the primary foundations of that stability have gone or been massively diluted."

This, in several respects, is surely an overstatement. For example, trade - central to the 1707 Anglo-Scottish Union - remains as important (if not more so) than three centuries ago, while aspects of the modern Union - not least the redistributive Barnett Formula and Welfare State - reveal deep links that didn't exist in the early 18th century.

So to conclude, as Sir Tom has, that there's "very little left in the Union except sentiment, history and family" seems rather odd. What about the BBC? Cultural institutions? A shared Parliament and Civil Service? He even cites the "weakening influence of the monarch", though not so weak that he felt compelled to turn down a (well-deserved) knighthood this year.

Devine's focus is naturally on the relationship between England and what he often calls "Scotia", which rather neglects the role of Wales and (Northern) Ireland in the multi-national UK. Linda Colley, another eminent historian, was careful to cite all four "home nations" during her Book Festival appearance, concluding that history pointed towards a more federal relationship rather than independence.

At the Book Festival today, meanwhile, the novelist James Robertson will also explore the role of culture and national self-confidence in the independence debate. He will make legitimate points about the degree to which politicians have avoided talking about culture (although many others, notably the National Collective, haven't been as reticent) and also the mythology of Scottish exceptionalism.

Robertson acknowledges - unlike some supporters of independence - that the Union has been largely benign in cultural terms, but also argues that the suppression of Highland culture in the 18th century had a long-term impact. His conclusion, unsurprisingly, is that Scotland "should be an independent country", part of which "would be building on the cultural confidence that we, as a nation, have".

As regular readers will know, I'm quite cynical about the so-called cultural argument for independence, not least because it appears to derive from a belief that Scottish culture is somehow stymied within the Union, an argument which, ironically, betrays a curious lack of confidence. Professor Alan Riach and the artist Sandy Moffat explored this view in another recent Book Festival session, though beyond the failure to promote the work of Allan Ramsay and Henry Raeburn, they didn't produce any compelling evidence of neglect.

Indeed, in choosing Allan Ramsay to make his point, Moffat ended up underlining a Unionist cultural case rather than a Nationalist one: Ramsay, for example, had a studio in Edinburgh but also a base in London, allowing him to exploit a wider market for his work. Similarly, Rona Munro's James Plays will enjoy an extended run at the National Theatre (of Great Britain) when the current Edinburgh International Festival run comes to an end. "Scottish culture" arguably benefits from as broad an audience as possible.

And the role of "confidence" also cuts both ways. Sir Tom Devine and James Robertson argue that the logical outcome of a more confident Scottish nation is independence, but equally that confidence could manifest itself as growing ease within an ever-changing Union.

As Allan Massie, like Robertson an acclaimed Scottish novelist, argues in the recent Saltire Society publication Nevertheless, his view of independence is also "a matter of self-confidence". If you fear that "in our global culture, Scottishness is too weak a thing to survive without the bulwark of an independent Scottish state", he writes, then a Yes vote makes sense, but if "you feel confident of Scotland's ability to remain Scottish and prosper in the Union", a No vote is equally logical.

If, as looks likely, a majority of Scots self-determine in favour of the Union on September 18 then I'd be interested to see the First Minister, Sir Tom Devine et al attribute that majority and democratic decision to a lack of confidence. After all, that's the inescapable corollary of such a (dare I call it patronising?) line of argument.