“Constitutions are intended to preserve practical and substantial rights, not to maintain theories.”

Source: Shouting Fire: Civil liberties in a Turbulent Age (2002), p. 34

Source: To run a constitution, 1986, p. 181

No. 78
The Federalist Papers (1787–1788)
Context: The complete independence of the Courts of justice is peculiarly essential in a limited Constitution. By a limited Constitution, I understand one which contains certain specified exceptions to the Legislative authority; such, for instance, as that it shall pass no bills of attainder, no ex post facto laws, and the like. Limitations of this kind can be preserved in practice no other way than through the medium of the Courts of justice; whose duty it must be to declare all Acts contrary to the manifest tenor of the Constitution void. Without this, all the reservations of particular rights or privileges would amount to nothing.

Napoleon : In His Own Words (1916)

Inaugural Address (4 March 1845)
Context: By the theory of our Government majorities rule, but this right is not an arbitrary or unlimited one. It is a right to be exercised in subordination to the Constitution and in conformity to it. One great object of the Constitution was to restrain majorities from oppressing minorities or encroaching upon their just rights. Minorities have a right to appeal to the Constitution as a shield against such oppression.

Attributed in Nassim Nicholas Taleb, Antifragile - Things that Gain From Disorder (2012), p. 213.
The earliest known appearance of this quote in print is Walter J. Savitch, Pascal: An Introduction to the Art and Science of Programming (1984), where it is attributed as a "remark overheard at a computer science conference". It circulated as an anonymous saying for more than ten years before attributions to Jan L. A. van de Snepscheut and Yogi Berra began to appear (and later still to various others).
Disputed, Misattributed

The earliest known appearance in print of this quote is Benjamin Brewster in the October 1881 - June 1882 issue of "The Yale Literary Magazine." Brewster asks, "What does his lucid explanation amount to but this, that in theory there is no difference between theory and practice, while in practice there is?" See page 202. https://books.google.com/books?id=iJ9MAAAAMAAJ&printsec=frontcover&vq=%22no+difference%22#v=onepage&q&f=false It has also been attributed by Doug Rosenberg and Matt Stephens (2007) Use Case Driven Object Modeling with UMLTheory and Practice p. xxvii as well as Walter J. Savitch, Pascal: An Introduction to the Art and Science of Programming (1984), where it is attributed as a "remark overheard at a computer science conference". It circulated as an anonymous saying for more than ten years before attributions to van de Snepscheut and Yogi Berra began to appear (and later still to various others).
Misattributed

Charles Evans Hughes, De Jonge v. Oregon, 299 U.S. 353, 365 (1937).
Judicial opinions
Context: Freedom of speech and of the press are fundamental rights which are safeguarded by the due process clause of the Fourteenth Amendment of the Federal Constitution. [... ] The right of peaceable assembly is a right cognate to those of free speech and free press, and is equally fundamental. As this Court said in United States v. Cruikshank, 92 U. S. 542, 552: The very idea of a government, republican in form, implies a right on the part of its citizens to meet peaceably for consultation in respect to public affairs and to petition for a redress of grievances. The First Amendment of the Federal Constitution expressly guarantees that right against abridgment by Congress. But explicit mention there does not argue exclusion elsewhere. For the right is one that cannot be denied without violating those fundamental principles of liberty and justice which lie at the base of all civil and political institutions — principles which the Fourteenth Amendment embodies in the general terms of its due process clause. [... ] These rights may be abused by using speech or press or assembly in order to incite to violence and crime. The people, through their legislatures may protect themselves against that abuse. But the legislative intervention, can find constitutional justification only by dealing with the abuse. The rights themselves must not be curtailed. The greater the importance of safeguarding the community from incitements to the overthrow of our institutions by force and violence, the more imperative is the need to preserve inviolate the constitutional rights of free speech, free press and free assembly in order to maintain the opportunity for free political discussion, to the end that government may be responsive to the will of the people and that changes, if desired, may be obtained by peaceful means. Therein lies the security of the Republic, the very foundation of constitutional government.

Address By Dr. Shanker Dayal Sharma President Of India On The Occasion Of The 50th Anniversary Of The First Sitting Of The Constituent Assembly