A few points of terminology should be highlighted here. First, whereas H.L.A. Hart persistently used the terms “rule” and “rules” in his writings, I much more often instead use the terms “norm” and “norms.” My reason for doing so is that Hart's employment of the former terms led Ronald Dworkin (in his early critiques of legal positivism) to infer mistakenly that Hart was differentiating rules from principles. Dworkin concluded that the jurisprudential model expounded in The Concept of Law would not encompass principles. To avoid the confusion engendered by Dworkin on that point, I will usually employ the word “norm” to denote a standard that is endowed with any degree of abstraction or specificity and with any degree of vagueness or precision. Still, I will sometimes use the word “rule” (or “rules”) as a synonym for “norm” (or “norms”).

Second, some of the occasions on which I do use the term “rule” in that manner are any junctures at which I am discussing Hart's notion of the rule of recognition. Because the phrase “rule of recognition” is such a specialized and well-known item of Hart's parlance, any substitution of “norm” for “rule” in that bit of his wording would be unhelpful. However, in order to signal the specialized character of his phrase, I have departed from Hart by using upper-case letters; in this book, as in quite a few of my other writings, I employ the label “Rule of Recognition” (rather than “rule of recognition”) to designate the fundamental standards for identifying the legal norms in any jurisdiction.

Third, in my penultimate chapter I also use upper-case letters to distinguish between the Rule of Law and the rule of law.1 Whereas the Rule of Law is a moral ideal that comprises the formal and procedural aspects of a liberal-democratic system of governance, the rule of law obtains whenever a legal system of governance exists (regardless of whether the system is liberal-democratic or authoritarian). Unlike the Rule of Law, the rule of law is not an inherently moral ideal.

Fourth, I use the terms “legitimate” and “permissible” – and “legitimacy” and “permissibility” – interchangeably throughout the book. Hence, a course of conduct CC is morally legitimate if and only if it is not in contravention of any moral duties. An ascription of moral legitimacy to CC does not per se indicate whether CC is also morally obligatory, nor does it per se indicate whether the adoption of CC will impose some moral obligations on anyone. All that can be inferred from such an ascription is that CC is morally not wrong.

Fifth, I employ the word “citizens” in this book to denote private individuals (including public officials in their capacities as private individuals). That word is not limited to the individuals in any jurisdiction who are full members of the polity there. It extends also to residents who are not such members. The operative contrast is not between citizens and other residents, but is instead between citizens and people who are acting in their capacities as officials.

Sixth, I use the following terms and phrases interchangeably: “viewpoint,” “point of view,” “perspective,” “standpoint,” “vantage point.”

Seventh, I use the term “valid” (or “validity” or “validly”) in two main ways. When I refer to the validity of norms as laws in a jurisdiction, I am following Hart in talking about the inclusion of those norms in the array of laws comprised by a system of governance. When I refer to the validity of an argument or an inference, I am talking about validity in the ordinary logical sense. That is, an argument is valid if and only if it cannot be the case that all the premises of the argument are true and its conclusion is false.

Any citations consisting solely of page numbers are citations to the second edition (1994) of The Concept of Law. Every citation to some other work – whether the work is by Hart or by anyone else – includes the year of publication. Each such citation also includes the author's surname if the identity of the author has not been clearly specified in the text.

I thank George Owers at Polity Press for commissioning this book in 2016, and I thank Julia Davies and Rachel Moore and Sarah Dancy at Polity Press for helping to steer the book through the process of production. I am also grateful to the two anonymous readers of the book proposal which I submitted in response to the commissioning invitation. Their comments were very helpful. Extremely helpful as well was an anonymous assessment of the antepenultimate version of the book. Equally valuable have been a number of conversations with one of my current PhD students, Jyr-Jong Lin. My reflections on the import of power-conferring norms and on Hart's intermittent neglect of that import have been greatly sharpened by my discussions with Jyr-Jong, whose own approach to such matters is interestingly different from mine.