Hart famously characterized the ‘essence’ of law as ‘the union of primary and secondary rules’. In doing so, he sought to draw our attention to the systematicity of legality. In a legal system, every primary rule is linked to every other rule by virtue of their common validation by the secondary rule of recognition. Legal systems, as opposed to, say, the norms of etiquette, are systems: the existence of any primary rule can always be traced to the very same source.
While Hart thought that systematicity distinguishes law from related phenomena, he does not go so far as to claim that it is unique in this regard. For it is clear that other normative systems also contain secondary, as well as primary, rules. Condominium associations have rules about who can change the rules of the condominium and which rules residents are required to follow. Condo by-laws are thus systematically interconnected in same way as legal rules are; yet, condominium associations are not legal systems. At best, the existence of secondary rules provides only a partial answer to the question ‘What is law?’ It constitutes the ‘essence’ of law in the ordinary meaning of the term, ie, the main idea or gist, rather than the technical, philosophical sense, ie, the complete set of properties the possession of which makes the object in question the thing that it is and not something else.
My aim in this paper will be to develop an account of the essence of law in the strict philosophical sense. In doing so, I will try to isolate the distinctive nature of legal institutions by contrasting them with closely related phenomena, such as parenting, clubs, organized crime, condominium associations and so on. I hope to show through this comparative process that legal systems are institutions of a very special kind: they are compulsory planning organizations that have a moral aim and bear a privileged relation to other planning organizations. I will claim that these properties constitute the essence of law insofar as their instantiation makes the law the law and not something else.
Shapiro, Scott J, The Planning Theory of Law (March 20, 2017).