As a phrase, the “rule of law” is a powerful rhetorical device. To condemn something as being “contrary to the rule of law” amounts to strong criticism. However, at least in popular discourse, the term is used loosely. This reflects two respects in which the rule of law, as a matter of both legal theory and constitutional reality, is both uncertain and contested. First, what is it that makes something contrary to the rule of law — in other words, what does the rule of law in the first place require? And, second, if something is contrary to the rule of law, what are the consequences of this? These questions boil down to asking what the rule of law is and what it does.

As far as the first question is concerned, there is broad agreement that the rule of law imposes two types of requirements. There is little, if any, dissent from the view that the rule of law implies what is sometimes termed a principle of legality, which demands that those who purport to exercise legal authority actually possess it. In this way, when a public body or a devolved legislature does something that causes it to exceed its legal powers, it contravenes the rule of law.

It is also generally accepted that the rule of law imposes a set of formal requirements as to the general characteristics of law and the legal system. These requirements are premised on the need for respect for human autonomy and dignity, which in turn demand that the law be publicly accessible, intelligible and applied in a predictable and principled manner by independent courts. On this basis, a law that, for example, operated with retrospective effect so as to criminalise already-committed conduct would breach the rule of law because criminalised individuals would have been denied the opportunity to make an informed choice as to whether they should remain on the right side of the criminal law. The removal of the facility for making such an informed choice fails to accord adequate respect to the individual’s autonomy and dignity, treating her as nothing more than the object of an authoritarian and arbitrary legal regime. A system that fails to accord with formal rule-of-law requirements is hardly a “legal” system at all.

However, a question that divides legal and constitutional theorists is whether the rule of law ought to extend to substantive requirements concerning the content of the law, as distinct from formal requirements pertaining to the general characteristics of legal rules and the legal system. Take, for instance, a piece of legislation providing for, or even requiring, discriminatory treatment on grounds such as sex or ethnicity. Such legislation could be drafted so as to comply with the rule of law’s formal requirements, by being clear, publicly accessible, prospective, and so on. But would it conform to the rule of law, given the egregious affront to human dignity implied by unequal treatment?

That depends on whether, in the first place, the rule of law speaks to the content as distinct from the general characteristics of legal rules — and, if so, on what grounds it does so. On this question, theorists’ views divide sharply. The intrinsic moral appeal of values like equality lead some writers to advocate a conception of the rule of law that is substantive enough to encompass such values. However, others, such as Raz, argue that “if the rule of law is the rule of the good law then to explain its nature is to propound a complete social philosophy”. In contrast, the formal conception, it is said, lays claim to a moral neutrality that may insulate it from a form of contentiousness that would erode its authority. The difficulty with this argument is that it is far from clear that the formal conception of the rule of law really is morally neutral. As noted above, it is itself animated by concern for human dignity and autonomy, and it is at least arguable that to permit such concerns to bite only upon law’s general characteristics as distinct from its content is to impose a somewhat arbitrary restriction upon the rule of law’s reach.

“Parliament does not legislate in a vacuum. Parliament legislates for a European liberal democracy founded on the principles and traditions of the common law. And the courts may approach legislation on this initial assumption.”
— Lord Steyn

Such philosophical disagreement can, of course, seem relentlessly abstract, and so the question arises whether any of this really matters. In other words, what practical, real-world difference, if any, does the rule of law make? As with the first question, concerning what the rule of law is, this second question, concerning what the rule of law can and should do, is the subject of disagreement amongst both academic commentators and judges. The extent of that disagreement increases as the debate shifts from more modest to more radical effects that the rule of law might have. A relatively modest effect, in respect of which there is general consensus, concerns the rule of law’s capacity to shape the courts’ interpretation of the law. Courts will thus prefer interpretations of statutory provisions that are more, rather than less, respectful of rule-of-law values. As Lord Styen said in the Pierson case: “Parliament does not legislate in a vacuum. Parliament legislates for a European liberal democracy founded on the principles and traditions of the common law. And the courts may approach legislation on this initial assumption.” Those common-law “principles and traditions” are (or include) the principles embodied in the rule of law. Of course, for as long as the Human Rights Act 1998 is on the statute book, the need for courts to have recourse to common-law rule-of-law principles is reduced, and so the debate about the extent of both the rule of law’s content and effect is made less pressing; but if, as is possible, the 1998 Act were to be repealed, such questions would assume a new urgency.

The less straightforward, and more contentious, matter concerns whether courts in the UK can go any further than interpretively safeguarding rule-of-law values. There are judicial dicta in cases like Jackson to the effect that it might be constitutionally possible for the courts to do so by, for instance, refusing to apply legislation that was contrary to a rule-of-law value. While there are no example of courts openly doing this, there are instances of courts adopting an interpretive approach to the protection of the rule of law that is so robust as to arguably shade into a judicial refusal to apply the legislation as enacted. The decision of the House of Lords in Anisminic and Lord Neuberger’s judgment in Evans are arguably examples of such an approach.

The upshot is that the outer limits of the rule of law’s effect are uncertain, because the relationship between it and the principle of parliamentary sovereignty is itself uncertain. Orthodoxy implies that the two principles sit in a hierarchical relationship with one another, sovereignty being at the top. After all, if Parliament is sovereign, it can do anything, including affronting the rule of law. Taken in combination, however, cases like Jackson, Anisminic and Evans suggest that such an analysis may be insufficiently subtle. They also suggest that there may not be a one-size-fits-all answer to this question precisely because the two questions considered in this post — concerning the content and effect of the rule of law — sit in relationship with one another. In other words, the extent of the effect of a given rule-of-law value may turn in part upon its fundamentality, those values that are regarded as particularly important being more likely to command the very boldest judicial protection. For this reason, among others, it is essential to think about these two aspects of the rule of law in tandem with one another. This does not make the rule of law easy to understand, but it at least helps to frame the parameters within which the issues fall to be debated.

Further reading