We know that, according to Austin, laws are general commands backed by sanctions. But that isn’t enough. There are lots of commands like that, but only some are laws.
Austin’s answer is that the commands come from the sovereign. Sovereignty, in turn, is understood in terms of habits of obedience.
Hart’s criticisms are aimed at showing that Austin needs to appeal to rules. Hart himself puts rules at the center of his answer to the “what is law?” question.
There were several inventive suggestions for saving Austin from Hart’s various objections. Any of them might work, but all play into Hart’s hands, in my opinion.
For example, Bernice and Sayre proposed that the habit of obedience is not given to a natural person. Rather, it is given to the “artificial” person of the office: the King, the President, etc. If so, there’s no problem in making the transition from Rex I to Rex II. The habit of obeying Rex II’s commands is the same as the habit of obeying Rex I’s. In both cases, the habit was best described as “obeying the king’s commands”; Rex I and Rex II just both happened to occupy the office.
Hart will ask: how do people identify the office? Suppose Rex II’s brother Bruce claims to occupy the office. How do the people decide whether their habit is to obey Rex II or Bruce?
Hart has an answer, but it goes beyond the basic elements that Austin tried to use. The answer, according to Hart, involves a rule for determining who is king. For example, the rule might be “each monarch shall be succeeded by his or her oldest surviving child”. Or it might be “the monarch shall be succeeded by his or her child bearing his or her name”. Or it might be “all monarchs must bear the name Rex”. But it has to be a rule. Habit alone won’t do the trick.
I think that he would say something similar in response to Victor’s suggestion that Austin jettison habits of obedience. Without those, Hart will say, we have to appeal to a rule to decide who is the sovereign.