A constitutional system includes, but is more than, the concept of the rule of law. A constitution is a meta-legal document, and takes the objectivity of ‘rule of law’ and raises to cover not only positive laws, but the entire structure and function of government.
Thus while the twelve tables of Roman law, the Decalogue of Moses, and Hammurabi’s code are all examples of rule of law, they are not constitutional systems.
Thomas Paine, writing in the 1790s, points out that a constitution is prior, both logically and temporally, to a government:
A Constitution is a Thing antecedent to Government, and a Government is only the Creature of a Constitution. The Constitution of a Country is not the act of its Government, but of the People constituting a Government. It is the Body of Elements to which you can refer and quote article by article; and which contains the principles upon which the Government shall be established, the manner in which it shall be organized, the powers it shall have, the Mode of Elections, the Duration of Parliaments, or by what other name such Bodies may be called; the powers which the executive part of the Government shall have; and, in fine, everything that relates to the compleat organization of a civil government, and the principles upon which it shall act, and by which it shall be bound. A Constitution, therefore, is to a Government what the laws made afterwards by that Government are to a Court of Judicature. The Court of Judicature does not make the laws, neither can it alter them; it only acts in conformity to the laws made: and the Government is in like manner governed by the Constitution.
Surveying the world of his time, specifically the constitutional system in the United States, the failed constitutional attempt in the French Revolution, and the quasi-constitutional accretion of texts and common law traditions in England, Paine ventures some general remarks about constitutional systems. He denies that England has, in the strictest sense of the words, a constitutional system; he argues that it is an ad-hoc compilation of legal thought over the centuries, and a poor defender of liberty.
Paine is broad-minded enough to consider that the United States Constitution is not the only conceivable or practical constitutional possibility. British philosopher A.J. Ayer writes:
Concluding that no further proof is needed to show that if governments are to serve the interest of a nation, they need the backing of a Constitution, Paine proceeds to consider what that Constitution should be. As one would expect, his proposals are mainly in accordance with the American Constitution, but not entirely so. There are at least two important points of difference.
Paine is willing to consider that the traditional tripartite division of power (legislative, judicial, executive) as we find it in, e.g., Montesquieu is not the only way to divide power. He argues for the possibility of having only two branches of government, the legislative and the executive. He is willing to configure the judiciary as a part of the executive.
In the legislative branch, Paine considers the possibility of a unicameral legislature to be as viable, and in his opinion occasionally superior, to a bicameral legislature.
It is not the specifics of any one particular constitution which caused Thomas Paine, and so many other thinkers of his era, to seek written constitutions as the foundations for government. Rather, it is the general idea of an objective and external text, publicly accessible, and approved by the citizens, which gives the notion of a written constitution its attractiveness.
It embodies both the notion of popular sovereignty and the rule of law. If the rules by which the government operates are objectively set down and published, then even if those rules are quirky, or even corrupt, there is a measure of equality inasmuch as every citizen is entitled to engage in both interpretive debate and parliamentary maneuvering.
That humans inherit the right to ‘pursuit of happiness’ is instantiated in the publication of the operative rules of government, and each citizen is entitled to his attempt to negotiate a path through those rules as best he can calculate.
But if the constitution is illegitimately changed, even in an effort to make it more “fair” by some definition, then the rule of law has been violated, and any good faith effort made to work within the system has been betrayed. Constitutional scholar Mark Levin writes:
If the Constitution’s meaning can be erased or rewritten, and the Framers’ intentions ignored, it ceases to be a constitution but is instead a concoction of political expedients that serve the contemporary policy agendas of the few who are entrusted with public authority to preserve it.
The constitution may be likened to the rules of a game. Consider a variety of games, from chess to poker, from tennis to checkers, from Monopoly to Parcheesi. Any change in rules, once the game has started, corresponds to our intuitive notion of “unfair.”
One might well imagine a discussion among four card players, or twenty-two soccer players, about altering the rules of the game once a tournament has begun. The majority would certain object to changing the rules in the middle of a game, and any serious attempt at implementing such a change would result, not in a more “fair” event by any intuitive sense of the word, but rather would result in chaos, anarchy, the end of the game, and a net loss to all players - ‘loss’ here being, at a minimum, the loss of the opportunity to participate, and potentially much more.
Constitutional government yields justice - again, in any reasonable and intuitive sense of that word - because it objectively and publicly externalizes the rules of government by posting them for inspection and thereby setting the field for discussion of them. There is no claim that a constitutional government is perfect, rather only that it is less flawed than any other form. But a constitution which can be changed ex post facto, either explicitly or by judicial interpretation of its words, fails to function as a limit or restraint on government.
If a constitution contains within itself a mechanism for its own legitimate change - an amendment process - then any other change, i.e. a change not authorized by its own internal mechanism, including a change introduced by redefinition of the words in its text, is a violation of every citizen.