H.L.A. Hart, answered from the texts and cited to the page.
The rule of change is one of the three secondary rules I identified as remedying the characteristic defects of a social order that relies on primary rules of obligation alone. The defect it addresses is what I called the static quality of such a regime. In a society governed only by primary rules, the sole mechanism by which rules alter is the slow organic process — conduct once optional becomes habitual, then obligatory; deviations once punished come to be tolerated, then pass unnoticed.1
There is no means of deliberately adapting rules to changed circumstances, no way to eliminate an old rule or introduce a new one by any act of will, because doing so would itself presuppose rules of a different kind.2 The remedy is the rule of change: a secondary rule that empowers an individual or body of persons to introduce new primary rules and to eliminate old ones.3
The simplest version merely specifies who may legislate and that their enactment counts. But rules of change may be considerably more complex — the powers they confer may be unrestricted or hedged in various ways, and the rule may prescribe in more or less rigid terms the procedure to be followed.4 There is, necessarily, a close connection between rules of change and the rule of recognition: wherever a rule of change exists, the rule of recognition will incorporate legislation as an identifying feature of valid rules, though it need not specify every procedural detail — an official certificate or copy will typically suffice as proof of due enactment.5
Rules of change also operate at the private level. The rules that confer on individuals the power to make wills, contracts, and transfers of property are, in structure, a form of rule of change — they enable individuals to vary their initial positions under the primary rules, exercising what Kelsen rightly saw as a kind of limited legislative power.6
A society without such private power-conferring rules would lack precisely the amenities that make life under law so different from life under a bare regime of obligation.7 The larger point is this: Austin's command theory, built from the elements of orders, obedience, habits, and threats, cannot yield the idea of a rule at all, and so cannot account for power-conferring rules of any kind.8
Rules of change confer powers; they do not impose duties; and that distinction — between rules that require conduct and rules that enable operations leading to the creation or variation of duties — is what Austin's framework has no resources to draw.9
The only mode of change in the rules known to such a society will be the slow process of growth, whereby courses of conduct once thought optional become first habitual or usual, and then obligatory, and the converse process of decay, when deviations, once severely dealt with, are first tolerated and then pass unnoticed.The Concept of Law, p. 103
There will be no means, in such a society, of deliberately adapting the rules to changing circumstances, either by eliminating old rules or introducing new ones: for, again, the possibility of doing this presupposes the existence of rules of a different type from the primary rules of obligation by which alone the society lives.The Concept of Law, p. 103
The simplest form of such a rule is that which empowers an individual or body of persons to introduce new primary rules for the conduct of the life of the group, or of some class within it, and to eliminate old rules.The Concept of Law, p. 106
Such rules of change may be very simple or very complex: the powers conferred may be unrestricted or limited in various ways: and the rules may, besides specifying the persons who are to legislate, define in more or less rigid terms the procedure to be followed in legislation.The Concept of Law, p. 106
Plainly, there will be a very close connection between the rules of change and the rules of recognition: for where the former exists the latter will necessarily incorporate a reference to legislation as an identifying feature of the rules... Usually some official certificate or official copy will, under the rules of recognition, be taken as a sufficient proof of due enactment.The Concept of Law, p. 106
many of the features which puzzle us in the institutions of contract or property are clarified by thinking of the operations of making a contract or transferring property as the exercise of limited legislative powers by individuals.The Concept of Law, p. 106
Without such private power-conferring rules society would lack some of the chief amenities which law confers upon it. For the operations which these rules make possible are the making of wills, contracts, transfers of property, and many other voluntarily created structures of rights and duties which typify life under law.The Concept of Law, p. 106
The root cause of failure is that the elements out of which the theory was constructed, viz. the ideas of orders, obedience, habits, and threats, do not include, and cannot by their combination yield, the idea of a rule, without which we cannot hope to elucidate even the most elementary forms of law.The Concept of Law, p. 91
Rules of the first type impose duties; rules of the second type confer powers, public or private. Rules of the first type concern actions involving physical movement or changes; rules of the second type provide for operations which lead not merely to physical movement or change, but to the creation or variation of duties or obligations.The Concept of Law, p. 91