Constitutionalism is "a compound of ideas, attitudes, and patterns of behavior elaborating the principle that the authority of government derives from and is limited by a body of fundamental law".Don E. Fehrenbacher, Constitutions and Constitutionalism in the Slaveholding South (University of Georgia Press, 1989). p. 81. .

Political organizations are constitutional to the extent that they "contain institutionalized mechanisms of power control for the protection of the interests and liberties of the citizenry, including those that may be in the minority". As described by political scientist and constitutional scholar David Fellman:

Definition Constitutionalism has prescriptive and descriptive uses. Law professor Gerhard Casper captured this aspect of the term in noting, "Constitutionalism has both descriptive and prescriptive connotations. Used descriptively, it refers chiefly to the historical struggle for constitutional recognition of the people's right to 'consent' and certain other rights, freedoms, and privileges. Used prescriptively, its meaning incorporates those features of government seen as the essential elements of the... Constitution".Leonard Levy, ed., Encyclopedia of the American Constitution, (Gerhard Casper, "Constitutionalism"), vol 2, p. 473 (1986) .

Descriptive One example of constitutionalism's descriptive use is law professor Bernard Schwartz's five volume compilation of sources seeking to trace the origins of the U.S. Bill of Rights.Bernard Schwartz, The Roots of the Bill of Rights (5 vols., Chelsea House Publisher, 1980) . Beginning with English antecedents going back to Magna Carta (1215), Schwartz explores the presence and development of ideas of individual freedoms and privileges through colonial charters and legal understandings. Then in carrying the story forward, he identifies revolutionary declarations and constitutions, documents and judicial decisions of the Confederation period and the formation of the federal Constitution. Finally, he turns to the debates over the federal Constitution's ratification that ultimately provided mounting pressure for a federal bill of rights. While hardly presenting a straight line, the account illustrates the historical struggle to recognize and enshrine constitutional rights and principles in a constitutional order.

Prescriptive In contrast to describing what constitutions are, a prescriptive approach addresses what a constitution should be. As presented by the Canadian philosopher Wil Waluchow, constitutionalism embodies

One example of this prescriptive approach was a project of the National Municipal LeagueFrank Mann Stewart, A Half Century of Municipal Reform: A History of the National Municipal League Ch.2 (Univ. of California Press, 1950). to develop a model state constitution.

Constitutionalism vis-à-vis Constitution The study of constitutions is not necessarily synonymous with the study of constitutionalism. Legal historian Christian G. FritzChristian G. Fritz, American Sovereigns: The People and America's Constitutional Tradition Before the Civil War. Cambridge University Press, 2008. distinguishes between "constitutional questions", examining how the constitution was interpreted and applied to distribute power and authority as the new nation struggled with problems of war and peace, taxation and representation, and "questions of constitutionalism —how to identify the collective sovereign, what powers the sovereign possessed, and how one recognized when that sovereign acted." He noted that "questions of constitutionalism could not be answered by reference to given constitutional text or even judicial opinions" but were "open-ended questions drawing upon competing views".Christian G. Fritz, American Sovereigns: The People and America's Constitutional Tradition Before the Civil War (Cambridge University Press, 2008). p. 6 .

A similar distinction was drawn by British constitutional scholar A.V. Dicey in assessing Britain's unwritten constitution. Dicey noted a difference between the "conventions of the constitution" and the "law of the constitution". The "essential distinction" between the two concepts was that the law of the constitution was made up of "rules enforced or recognised by the Courts", making up "a body of 'laws' in the proper sense of that term." In contrast, the conventions of the constitution consisted "of customs, practices, maxims, or precepts which are not enforced or recognised by the Courts" but "make up a body not of laws, but of constitutional or political ethics".Dicey, A. V., Introduction to the Study of the Law of the Constitution. , 8th ed. (London: Macmillan 1914) (Part III: The Connection between the law of the constitution and the conventions of the constitution; Ch 14.

Core features

Fundamental law and legitimacy of government One of the most salient features of constitutionalism is that it describes and prescribes both the source and the limits of government power derived from fundamental law. William H. Hamilton has captured this dual aspect by noting that constitutionalism "is the name given to the trust which men repose in the power of words engrossed on parchment to keep a government in order."Walton H. Hamilton, "Constitutionalism". in Edwin R.A. Seligman, et al. (eds) Encyclopedia of the Social Sciences (New York: Macmillan 1931). p. 255.

Moreover, whether reflecting a descriptive or prescriptive focus, treatments of the concept of constitutionalism all deal with the legitimacy of government. One recent assessment of American constitutionalism, for example, notes that the idea of constitutionalism serves to define what it is that "grants and guides the legitimate exercise of government authority".Christian G. Fritz, American Sovereigns: The People and America's Constitutional Tradition Before the Civil War (Cambridge University Press, 2008). p. 1. . Similarly, historian Gordon S. Wood described the most "advanced thinking" on the nature of constitutions wherein the constitution was conceived (according to Demophilis, who was possibly George Bryan) a "sett of fundamental rules by which even the supreme power of the state shall be governed."Gordon S. Wood, The Creation of the American Republic, 1770–1787 (Norton & Co. 1969). p. 268. (quoting Demophilus, Genuine Principles. . p. 4> (Demophilus [George Bryan?]: the Genuine Principles of the Ancient Saxon, Or English [,] Constitution). Ultimately, American constitutionalism came to rest on the collective sovereignty of the people, the source that legitimized American governments.

Civil rights and liberties Constitutionalism is not simply about the power structure of society. It also asks for a strong protection of the interests of citizens, civil rights as well as civil liberties, for all, and has a close relation with democracy. The United Kingdom has several centuries-old laws limiting governmental power (for example, the Bill of Rights 1689). Historically, there has been little political support for introducing a comprehensive written or codified constitution in the UK. However, several commentators and reformers have argued for a new British Bill of Rights to provide liberty, democracy and the rule of law with more effective constitutional protection.Abbott, Lewis F. Defending Liberty: The Case for a New Bill of Rights. ISR/Google books, 2019.

Criticisms

Legal scholar Jeremy Waldron contends that constitutionalism is often undemocratic:

Libertarian political theorist Murray Rothbard criticized constitutionalism as being incapable of restraining governments and not protecting the rights of citizens from their governments: It is true that, in the United States, at least, we have a constitution that imposes strict limits on some powers of government. But, as we have discovered in the past century, no constitution can interpret or enforce itself; it must be interpreted by men. And if the ultimate power to interpret a constitution is given to the government's own Supreme Court, then the inevitable tendency is for the Court to continue to place its imprimatur on ever-broader powers for its own government. Furthermore, the highly touted "checks and balances" and "separation of powers" in the American government are flimsy indeed, since in the final analysis all of these divisions are part of the same government and are governed by the same set of rulers.Murray N. Rothbard, For a New Liberty: The Libertarian Manifesto (1978), p. 48.

Constitutionalism by nations Used descriptively, the concept of constitutionalism can refer chiefly to the historical struggle for constitutional recognition of the people's right to "consent" and certain other rights, freedoms, and privileges. On the other hand, the prescriptive approach to constitutionalism addresses what a constitution should be. Two observations might be offered about its prescriptive use: Observation 1 (Assumption of constitutionalism) There is often confusion in equating the presence of a written constitution with the conclusion that a state or polity is one based upon constitutionalism. As noted by David Fellman, constitutionalism "should not be taken to mean that if a state has a constitution, it is necessarily committed to the idea of constitutionalism. In a very real sense... every state may be said to have a constitution, since every state has institutions which are at the very least expected to be permanent, and every state has established ways of doing things". But even with a "formal written document labelled 'constitution' which includes the provisions customarily found in such a document, it does not follow that it is committed to constitutionalism...."