IMAGINE we could run experiments in politics as we do in science. Imagine for a moment that we could create another country as much like Scotland as possible – similar size, similar population, similar climate, similar culture.

Now imagine that we could, with these two Scotlands, run tests. We could allow one to become independent and keep the other one in the United Kingdom.

Over time, we’d begin to see the pros and cons of each constitutional arrangement, played out in the daily lives of citizens.

GDP/capita is a flawed measure of economic progress, as Nicola Sturgeon did well to remind us at a recent TED Talk, but we could look at the two Scotlands across a basket of other, more meaningful, outcome measures. We could ask about child poverty rates or life expectancy. We could ask how many nuclear weapons each Scotland has, or how many of its citizens died in the Iraqi desert, or whether their citizens have the right to live and work across the EU.

Ultimately, we must judge constitutions by their effects. When we see ill-effects around us – corrupt politicians, with corrupt ethics, pursuing corrupt policies, for corrupt reasons, by corrupt means – we can be fairly sure that beneath the surface lies a constitutional failure.

As Thomas Paine put it: ‘‘When it can be said by any country in the world, my poor are happy, neither ignorance nor distress is to be found among them, my jails are empty of prisoners, my streets of beggars, the aged are not in want, the taxes are not oppressive, the rational world is my friend because I am the friend of happiness. When these things can be said, then may that country boast its constitution and government.’’ Or, as another radical activist said 1800 years earlier: ‘‘By their fruits shall ye know them.’’ Unfortunately, we cannot create a second Scotland as a test bed. But there is another country just next door. Ireland is not identical to Scotland, but it is sufficiently similar to make the comparison interesting.

We’ve been Ireland-gazing for a while now. In some ways it started with the Celtic Tiger boom (which bust, but quickly pulled itself out of the mess) and continues as we watch Brexit unfold.

Ireland is strong. It has powerful allies in Europe. It is respected on the world stage. None of that can be said for the UK anymore.

And it just so happens that Ireland has a truly fascinating constitutional history. The first proper constitution of Ireland (leaving aside the short interim constitution adopted by the First Dáil in 1919) was the Irish Free State Constitution of 1922.

This constitution was constrained by the terms of the Anglo-Irish Treaty, which gave Ireland independence on dominion-like terms within the Commonwealth.

It did not, however, simply replicate “Westminster in miniature”. The lower house was elected by single transferable vote.

There was a short but innovative bill of rights, including freedom of religion, speech, assembly and association, guarantees of personal liberty and trial by jury, and freedom from religious discrimination.

The prime minister was not chosen from on-high by the Crown, as in other dominions, but democratically nominated by the lower house. All good sensible reforms.

Yet the Free State Constitution has one fatal flaw: it could be amended unilaterally by ordinary parliamentary majorities. This lack of entrenchment was the undoing of the whole structure. In 1931 the government pushed through a Public Safety Act that gutted the guarantees of basic rights and instituted a draconian system of military courts instead.

The current Irish constitution, adopted in 1937, fixed this problem. It can be amended only by referendum. It is in this sense that the Irish people really are free and sovereign – their fundamental constitutional rights and democratic guarantees cannot be changed without their consent.

In recent years, Ireland has seen a flurry of successful constitutional referendums – on same-sex marriage, abortion, divorce and blasphemy. These all tend towards an incremental but profound renegotiation of the Irish constitutional order, from one based on interwar theories of Catholic democracy to one founded on secular concepts of rights.

The crucial point is that these changes have not been imposed. They have been publicly debated and voted upon by a people who have acquired a strong sense of their own constitutional sovereignty.

And it is perhaps no surprise that Scotland has copied the successful Citizen’s Assembly process used in Ireland.

That said, Scotland is not Ireland. Every country’s constitution has unique features for unique circumstances. But Ireland’s constitutional trajectory is a good mirror, in which we see both a warning and an example.

The Free State Constitution warns us of the dangers of relying on an unentrenched constitution, amendable by ordinary parliamentary majorities. The current Irish constitution, in contrast, provides a practical tangible lesson for Scotland of a constitutional democracy that could bring the Claim of Right’s concept of popular sovereignty to life.

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