THE sports to which I gravitated in my youth were all a bit niche: cricket, horse riding, rowing, fencing, shooting and sailing. I never really got into football. I’m delighted for the Scotland women’s team in their recent performance, but I’m some way out of my depth on the subject of football.

This is said by way of a disclaimer, because this column is mainly about the offside rule. I might not know everything about football, like some referees apparently, but I do know a thing or two about rules – especially those bundles of rules known as written constitutions that most modern democracies are based upon.

Regular readers of this column will be familiar with the concept of a written constitution as a supreme and fundamental law. A written constitution is supreme in status, in the sense that it is superior to ordinary law and can only be changed by a special process.

It is fundamental in content, in that it declares the fundamental principles on which the state is based, protects the fundamental rights of citizens, and regulating the fundamental institutions and processes of democratic self-government.

The need for a written constitution in an independent Scotland has also been thoroughly reiterated. A written constitution is the norm – not only in Europe, but also throughout the Commonwealth. In the modern world, having a written constitution is not an optional extra: it is essential to be taken seriously. Only a written constitution can provide the guarantees we need to ensure that an independent Scotland will be a democratic Scotland: a country where elections are free and fair, where parliamentary government flourishes, where human rights are protected, the integrity of the civil service and the independence of the judiciary upheld, and where all minorities are secure.

A constitution reassures both foreign and domestic audiences that an independent Scotland can be trusted, both to be a good steward of the common good internally and a friendly neighbour externally.

There is, however, one frequently-cited objection to the idea of a written constitution: that it precludes future changes, locking in today’s wisdom and excluding tomorrow’s.

What right have we to bind future generations? What authority will a constitution have 30 years, 50 years, 100 years, after it has been adopted? How will it respond to new challenges, the nature of which cannot be predicted?

This objection is based on a misunderstanding. A constitution is harder to change than ordinary law – so it cannot be easily or unilaterally changed by the government of the day – but that does not mean that it is incapable of change.

Some constitutions do contain “eternity” provisions, but that is not necessary or normal practice. Most constitutions can be changed according to the amendment process they describe – typically some combination of time delays, intervening elections, supermajorities, ratification by state legislatures, and referendum requirements.

The often-criticised US Constitution is unusually rigid, requiring a two-thirds majority in both Houses of Congress plus ratification by three-fourths of the states. The Irish Constitution, in contrast, is unusually flexible; it needs only an ordinary parliamentary majority – but this must be ratified by the people voting in a referendum. Most constitutional amendment rules fall between these extremes, with a two-thirds parliamentary majority (with or without a referendum) probably being most common.

Many constitutions have different levels of rigidity, giving a graded balance between guarantees and flexibility.

The South African constitution can be amended by a two-thirds majority in Parliament, but its fundamental values – human dignity, equality and human rights, non-racialism and non-sexist, the supremacy of the constitution and the rule of law, and multi-party democracy based on universal suffrage – can only be amended by a three-fourths majority.

In other words, change is not precluded. A constitution does not bind future generations. It only binds future governments or narrow parliamentary majorities. It ensures that any change is properly considered and broadly agreed – as it should be.

The SNP’s 2002 ‘‘MacCormick draft’’ proposed a simple yet effective constitutional amendment formula: it could be changed by a three-fifths majority vote in Parliament, followed by majority approval in a referendum. Under normal circumstances, this would mean that no governing party would be able to change the constitution alone. A cross-party consensus would have to be reached in Parliament and then ratified by the sovereign people.

So, back to football. The offside rule has been changed several times in this history of football. Having clearly written rules does not prevent the development of the game. But the rules cannot be changed by the players on a whim.

The alternative – the British system of parliamentary absolutism – gives the team in possession of the ball the power to change the offside rule at its own convenience. You do not have to be a football fan to realise that’s an absurd state of affairs.

This column welcomes questions from readers