Most people in Western countries, one would like to think, see great value in the democracy they enjoy. Rather fewer, perhaps, attach similar importance to the rule of law.
Yet it is the rule of law that guarantees our freedom from the exercise of arbitrary power.
It was the great Chief Justice, Sir Edward Coke, who established early in the 17th Century the fundamental principle that no man - not even the King - is above the law.
At that time, the King saw himself as the Government, and believed that his supposedly divine right to rule meant that he could not be constrained by the law.
Coke's great principle is still alive today, and more important than ever. Governments still try from time to time to behave as autocrats - and indeed, they find it easier in some ways to do so than did the Stuart kings. In a modern parliamentary democracy, governments can constitute an "elective dictatorship", able to rely on their parliamentary majority to enforce their will.
A compliant Parliament can allow the executive a virtually free hand.
Step forward the courts. It is the courts that will ensure that governments, even if they dominate Parliament, cannot overstep the mark. Over the centuries, the courts have developed a range of remedies to protect the ordinary citizen when governments behave in an arbitrary fashion.
One of the earliest such remedies was the ancient writ of habeas corpus which required public authority, in whatever guise, to give up "the body" - that is, to release a person who was being held illegally.
Since then, a whole body of law, known as administrative law, has been developed to rein in public authorities that exceed their legal authority; as an Oxford law don many years ago, I had the great privilege of making a small contribution to that development.
It is this body of law that ensures that a Government minister who makes a decision affecting private rights will have to stay within the law. He will find his decision struck down if it is biased, or is made to suit himself, or if he fails to listen fairly to all sides, or he takes account of irrelevant factors or ignores those that are relevant, or behaves or decides unreasonably, or makes a legal error, or exceeds the powers he can lawfully exercise.
The courts stand ready, at the request of an individual citizen, to conduct what is called a "judicial review" of decisions that might be vitiated by any of these errors and to make sure that governments cannot simply say "we are the Government - we can do what we like."
Parties to a private legal dispute who are displeased by a decision reached by the courts will sometimes rail against what they think of as the "rule of law", believing that it does not serve them well.
But the rule of law has a particular meaning and describes the principle that the courts will guarantee to each one of us equality before the law and will stand as a bulwark between the ordinary citizen and public power exercised illegally.
Does any of this matter any more? Yes, of course it does, especially when the power of Government now reaches into every aspect of our lives. And we have just seen a striking current example, not here in New Zealand, but in the United States.
The new US President appears to believe that he can make the law all by himself and cannot be challenged. When the courts declared that his executive order banning entry to people from seven predominantly Muslim countries had exceeded his powers and had discriminated illegally, he showed his ignorance of the US Constitution by attacking the courts for "usurping power", as if they had no business in making sure the law was observed.
He seems unaware that the law is not made merely on his say-so. Much as he seemed to relish signing his "executive orders" with the television cameras rolling, those orders must be made in a proper exercise of his legal powers. If a would-be autocrat tries to exercise powers he does not have, every citizen needs to know that the courts will strike him down. We can all rest more easily under the rule of law.
Bryan Gould is a former British MP and Waikato University vice-chancellor. He writes an occasional column on current events.