Geoffrey Palmer and Andrew Butler’s new book,             A Constitution for Aotearoa New Zealand, is excellent. I definitely don't agree with all of its contents, but it certainly provides food for thought. And when it comes to New Zealand's constitution, that can only be a good thing.

One of the things it has got me thinking about, at least, is how we should think about the difference between written and unwritten constitutions. Unlike some constitutional scholars I think there is a difference, and Geoffrey and Andrew must agree or they would not have written their book. But it is a difficult thing to get a grip on. So, I have come up with three, relatively accessible ways to think about the key differences.

First off, I think it can be helpful to think of constitutions in architectural terms. A written constitution focuses on the things it can describe, which tend to be the formal features of law and government. It tells you where the foundations are, and what they’re made of. It tells you where the walls go (because it’s important to keep the kitchen and the wash room separate). And it tells you how the roof should be constructed, to protect the entire edifice.   

These are all important things, and they concern an unwritten constitution too. But an unwritten constitution approaches things differently. Instead of focusing on the floors, walls and ceilings, the first thing it takes into account is the spaces in between those structures. It gives some thought about how people interact within the constitutional spaces we create, and the things they want to get done. Trying to ‘write down’ what a space for interaction looks like is understandably a bit challenging, which is why written constitutions focus on tangible things like walls and floors. But in doing so they might risk overlooking something.

A second way to think about constitutions is in terms of their informational - or instructional - dimension. I think it is helpful to think of written constitutions as a kind of map. If you are exploring a foreign city, a good map will set out the key features in a visual way that helps you navigate strange streets and find unfamiliar buildings. Maps help us get where we want to go by following a definite path. And while all maps abstract from reality to some extent, they are a very accurate way of understanding the terrain.

If written constitutions are like maps, unwritten constitutions might be more like guide books. A guide book won't tell you where ever street is, but they are very good if you want to pick up a few tips and tricks to navigate the interactions with the locals. What are the customs you should observe? How do you greet people, or show appreciation. Maps won't tell you any of this, but a good guide book might. Of course, you need a dose of common sense and a willingness to give it a go to be successful, and you don’t always know where you’ll end up. But you can have some confidence knowing roughly how things in a foreign city actually work.

A third way to think about constitutions is in terms of personalities. A written constitution might be understood as an extroverted constitution. It lets you know what its thinking, its assertive, it lets you know clearly when you’ve crossed a boundary. It signals loud and clear what’s going on and what will happen as a result. An unwritten constitution is more like an introverted constitution. It is reflective, and perhaps a bit enigmatic, and it considers the consequences of actions carefully. It doesn’t signal its inner workings as clearly, so you might need to ask it what its thinking. But if you do, and you’re patient enough, you are likely to get a satisfying response.

Each of these ways of thinking about written and unwritten constitutions tend towards caricature. To be sure, every real-world constitution needs to balance these aspects of written or unwritten constitutions carefully. But even just thinking about the differences is a good start. Hopefully these comparisons offer some food for thought.