We know that Austin’s theory is that laws are commands and Hart’s theory is that they are rules. Today we get the whole story: Hart thinks that law is the union of primary and secondary rules.
We talked about the distinction between primary and secondary rules and about the most important of secondary rule: the rule of recognition.
Primary and secondary rules
Primary rules are rules for behavior: Austin’s commands are an excellent example of primary rules. Secondary rules are rules about, well, rules. They concern how to make, modify, and interpret rules. He proposed three kinds of secondary rules.
The rule of recognition is used to identify the rules that are laws and distinguish them from those that are not laws.
Rules of change are used to make and alter laws.
Rules of adjudication are used to settle conflicting interpretations of the law.
For example, in our society, rules passed by Congress and signed by the President are recognized as law because the Constitution says they are (Article 2, Section 7). The Constitution is clearly part of our laws, but its rules do not involve commands or sanctions. Similarly, we recognize judges as having the authority to interpret laws and settle disputes about them. They get this authority from other laws that give them this authority. But the laws that create the judiciary do not seem to be commands or useful guides to predictions.
The rule of recognition
The rule of recognition is the most important secondary rule. It is what the members of society follow when they try to answer the question “what is the law?”
We tried to spell out the rule of recognition for our society by listing either things that are laws (statutes, e.g.) or sources of laws (the legislative acts and judicial decisions). We had some uncertainty about the Constitution. Is it a law (or set of laws) or is it a source of laws? Maybe both.
The upshot of this is that since there are several sources of law in our system, our rule of recognition is complex. Hart lists several possible sources of law as an example: authoritative texts, legislation, customary practice, commands from someone like a sovereign, past judicial decisions, or a constitution (Hart  1994, 100–101). As far as I can see, they are all recognized in our society.
We ended with trying to find out where the limits of our legal system are. What kind of change in our most basic legal rules would be so drastic as to bring the system to an end? The point of this was supposed to illustrate a point about the rule of recognition, namely, that it works only if it is accepted. The rule of recognition is not derived from other legal rules; in fact, it couldn’t be. It only exists if people believe it does. Once a significant portion of society no longer believes that there is a rule for identifying laws, there is no rule of recognition for that society.
These are the things you should know.
The difference between primary and secondary rules
The three secondary rules
Why the rule of recognition cannot be derived from any other legal rules. (If you know that, you know how the rule of recognition works.)
Hart, H. L. A. (1961) 1994. The Concept of Law. 2nd ed. Oxford: Clarendon Press.