IN his inauguration speech, Joe Biden admitted “I know speaking of unity can sound to some like a foolish fantasy.”

As if to confound him, there was a general consensus that it was a pretty good speech, though mainly because it wasn’t being made by Donald Trump, and thus managed to maintain some relationship with coherent expression and objective reality.

Mr Biden’s worry about unity is topical while so many Trump supporters continue to believe, on no evidence at all, that the election was a fix. But it isn’t an absolute truth (the speech was, in another break with the Trump era, pro-truth).

There have been plenty of relatively united societies; even, notwithstanding its racial and economic divisions, the US in happier times. None was perfect, but they could be workable; what Mr Biden was referring to when he began by talking of the “triumph of… the cause of democracy”. But that exposes a problem with the generally sunny view he advocated, because it is not clear that you can invariably have societies that are largely united and democratic.

In fact, the political structure of the United States (in common with most liberal Western democracies) was specifically designed to cramp democracy to some extent: just as the constitution was designed to keep the legislature, the executive and the courts in balance, it was intended to be a safeguard against populist tyranny.

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Most free countries have similar set-ups and principles, that can usually be traced to a greater or lesser extent to things like the Common Law (or Dicey’s interpretation of it), aspects of the French revolution, or thinkers of the Enlightenment such as Locke, Hume, Mill, Rousseau, and America’s founding fathers themselves.

This has worked, to the extent that the transition of power from Mr Trump to Mr Biden was – if, disgracefully, not entirely peaceful – at least something that happened. The system thwarted dictatorship. But you may think that, even if it’s a relief, isn’t all that much to boast about. Most of us would say it’s the bare minimum; it certainly isn’t a recipe for unity.

The reason is that Mr Trump’s supporters’ main quibble is with the system. “Draining the swamp” was a metaphor for ditching most of how American politics functioned. That’s not even all that new an idea – things like term limits were previous efforts to curtail political elites.

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They are not confined to America but pretty well universal in developed nations. Any system is bound to operate for the benefit of particular groups. For most of the post-war period in the West, that has meant a fairly centrist political class, government bureaucracies and corporations; in other words, the establishment. By definition, any system favours the establishment, because it creates one and is then sustained by it.

That’s all well and good while most people believe in it or at least tolerate it. Change can be made gradually by vague mainstream consensus – even a divisive, ideological, reforming politician such as Margaret Thatcher could only shift the UK in the direction she wanted by getting elected and getting policy past parliament (including her own party). Extreme challenges to the status quo, such as those advocated by, say, the Socialist Workers’ Party, tend for that reason to remain on the fringe. It’s also why revolutionary movements of both the Left and Right, when they gain power, don’t set up democracies.

It is often claimed that Nordic countries veer further towards social democracy, high taxes and welfare spending than many other societies because they are very homogeneous. But a paradox of such liberal countries is that unity can encompass some diversity: tolerance, the great essential for liberalism, includes judgmental disagreement – indeed, it implies it – but needn’t be divisive. It does, however, require general acceptance of the established order, even if that evolves over time.

Countries can function without being democracies (as many do, even if most of us wouldn’t like to live in them) while their populations do not chafe at their constraints. But it’s also true that countries cannot be united, even if they are democracies, when the point of division is one that requires change that the system cannot tolerate.

This has nothing to do with the merits of the case. Many of Trump’s supporters base theirs on lies, but there is nothing unreasonable, in and of itself, about claiming the US political system is broken (it’s what Bernie Sanders claims, too). But it’s not a unifying argument if you think that unity depends on subscribing to the existing system.

In the same way, you can make arguments for and against the UK being in the EU, including gradualist ones, such as being out of it, but in the EEA. You can postpone the decision or, at decent intervals, reverse it. But you can’t unite people who are opposed on the issue if you force the point, and democracy, sooner or later, involves forcing the point.

That’s why I’m sceptical about Gordon Brown’s view that division can be avoided and trust restored by tinkering with the UK’s political structures. If you think that the UK is the problem, that won’t unite anyone.

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If democracy solved this, then both sides of the independence debate would now be united on the result of the last referendum. If the system prevented division, there would be no question of a new mandate, no matter how many SNP MSPs get elected, because under the existing structure the issue isn’t within Holyrood’s competence.

That is hardly to be expected. Nationalists have every right to continue arguing their case, even if you think they ought to leave it for a while. That’s what those who wanted Britain to join the EEC had to do for decades in the post-war period, and then those who wanted it to leave had to do, over the decades since.

But, as the Brexit referendum and its aftermath showed, division was inevitable when the issue went to a vote. Unless and until an issue goes away of its own accord (as, for example, demand for independence did in Quebec), you can either have the unity of accepting an existing democratic decision or the division of forcing the choice again. You can’t have both.

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