The constitution of a government is the body or collection of rules and principles in accordance with which the powers of that government are exercised ; and a constitutional government is one the powers of which are exercised in accordance with rules and principles which are generally accepted as binding upon it and usually followed. In this proper and usual sense all the governments of civilized peoples are constitutional, whether they be monarchical or republican. If the body of rules and principles is not reduced to definite and authoritatively written form, the constitution is said to be unwritten, as in the familiar case of Great Britain. The body of rules and principles defining the nature of the British government and prescribing the persons who exercise authority under it and the scope of such authority is to some extent declared in statutes which are a part of the written law; to a further extent is composed of rules of law recognized by the courts, without any written basis, and therefore a part of the unwritten law; and to a still further extent consists of conventions or customs which though generally recognized and followed, do not have the force of law. An example of a statute which is regarded as a part of the constitution is the Habeas Corpus Act (1679) which declared more fully the duty of those holding persons under commitment for criminal offences to make prompt response to orders of the judges to show the nature of the authority under which the prisoner was detained, in order that the lawfulness of the detention might be judicially inquired into. (See below, § 241.) One of the rules of the unwritten law which is regarded as a part of the constitution is the principle that the king can do no wrong, and that his ministers, or others pretending to act under his authority, are themselves personally accountable for any violation of law, even though committed, as a matter of fact, under the king's command. A constitutional custom which has not the force of law may be illustrated by the practice that the cabinet, composed of various ministers acting as the king's advisers, and administering particular offices or departments of the government, must act as a body and must resign when they no longer have the support of Parliament. Such a practice is not prescribed by any statute, nor would any court attempt to enforce it as a part of the unwritten law. But it is fully recognized as one of the principles in accordance with which the government of Great Britain is conducted.

The constitution of Great Britain as a whole is, therefore, unwritten in the sense that it is not reduced to any definite and authoritative statement, although as a whole or in parts it has been expounded and explained by authors who have written on the subject, and who have stated, with more or less fulness and accuracy, its rules and principles. Some important English statutes, besides the Habeas Corpus Act already referred to by way of illustration, are constantly treated as parts of the constitution. The most notable of these is Magna Charta, which received the royal approval of King John in 1215, and, with slight modifications, was reapproved by many of his successors. Another is the Petition of Right, which was addressed by Parliament to Charles I. in 1628, and received his approval. And still another is the Bill of Rights, which regulated the descent of the crown, and also declared certain fundamental rights of the people as against the royal power, which was enacted by Parliament in 1689, and received the royal assent. These statutes are in form not different from other statutes which are a part of the written law of England, but the nature of their provisions is such as to properly characterize them as important parts of the English constitution, and no attempt is ever made to repeal them. As parts of the written law, such statutes as these are of course binding on the courts.

In the United States the constitutions of the various states and of the federal government are formally written and rest upon the will of the people expressed directly, through their chosen representatives, and are regarded, therefore, as having a higher authority than that of statutes enacted by the legislatures, created and existing in accordance with the provisions of the constitutions, or of executive acts authorized by the constitutions. These constitutions are not only laws of the states and the federal government respectively, and therefore a part of the written law, but they are superior to the ordinary statutory law. Constitutional Law in the United States, therefore, is concerned with the history and interpretation of certain formal written instruments, and not merely with the exposition of general and unformulated principles of government. Strictly speaking, constitutional law, as the term is used in this country, takes no account of mere practices and usages, no matter how generally observed, but is based on the language of written constitutions, and takes into account statutes, treaties, executive acts and regulations, and the decisions of the courts applying their provisions to specific cases.

Although the authority of a state or federal government is to be determined by the provisions of the written state and federal constitutions, and not from any mere general principles or constitutional rules recognized in this country or in England, nevertheless a written constitution is, like a statute, subject to interpretation, and must be applied to new circumstances and conditions by determining the true intent and purpose of its provisions. Nowhere is there any authority, however, to add to those provisions or to eliminate any portion of them, or to give them a meaning not reasonably within the intent with which they were framed, save by a formal amendment, as authorized in the constitutions themselves. Some text writers and a few judges have assumed that there is back of the written constitution a general unwritten constitution, somewhat analogous to that of Great Britain, serving as a limitation on the exercise of the powers of government as denned by the written instruments. This position is untenable and dangerous. If the written constitutions do not express the will of the sovereign people with reference to the distribution and limitations of the powers of government, but such will is to be ascertained from other sources, then we are practically in the same condition as the people of Great Britain and have no authoritative constitution. Furthermore, it is a fundamental principle of our constitutions that they have a higher authority than the corresponding general principles of the British constitution. Any act of the British Parliament supersedes previously existing rules and usages, however long established; while our constitutional provisions are effective as a definition of and limitation upon the powers of each branch of government, so that acts of any branch in excess of the power given to or in violation of limitations imposed upon it are invalid and of no force. To give to general principles and rules not found in a written constitution the force and effect of nullifying any action of a branch of the government which is not contrary to the written terms of the constitution, would be to assume that elsewhere than in the constitution-making power there is a power to limit and define the authority of branches of government created under the constitution. But no such authority can be found anywhere in our constitutional system. On examination it will be seen that what have been referred to as rules and principles of an underlying unwritten constitution are either on the one hand clearly implied in the provisions of the written constitutions themselves and therefore a part of them, as binding and effectual as though written in words; or on the other hand are mere general and well-recognized usages such as are said to be constitutional under a government like that of Great Britain, having no written and authoritative constitution, but which should not, where there is an authoritative constitution, as with us, be deemed any part of constitutional law.

Examples of such usages which have been so fully recognized that they might, if we had no written constitution, be said to be a part of the unwritten constitution, are the following: That no president shall be elected for more than two successive terms; and that the presidential electors shall vote for the candidate of the party on whose ticket they are selected. But it is evident that these so-called rules are not a part of our constitutional law. The limitation of the presidency to two terms for any one person furnishes a strong argument against the nomination or election of a president for a third term, an argument which has heretofore, as in the case of President Grant, been sufficiently potent to prevent renomination for a third term. But no one would pretend that, if such limitation were ignored and a president nominated and elected for a third term, he would not be lawfully president of the United States and have all the authority of president. No congress or court would venture to say that his election was for that reason not valid. Likewise there have been emergencies, such as the death before nomination of a candidate for president, which made it absolutely necessary for the electors chosen on a national party ticket to cast their votes for some one not nominated on such ticket, as in 1872, when Horace Greeley, the regular nominee of the Democratic party, died before the electoral vote was cast, and the electors in states in which the democratic ticket had a majority of the votes were compelled to exercise a discretion as to the candidate for whom their choice should be expressed. It could not have been contended for a moment that votes thus cast should not be counted for the person designated, although he was not the nominee of the party. Any such general rules and principles, therefore, though they may be said in some sense to be a part of the unwritten constitution under our form of government, are not of equal authority with the provisions of our written constitutions and are not in a legal sense limitations on the powers of government. They are analogous to those portions of the unwritten constitution of Great Britain which are of no binding and legal effect, although representing the general customs and usages in accordance with which that government is administered.

In Great Britain no acts of Parliament regularly adopted can be said to be unconstitutional in the sense of being invalid and without legal effect. It may be urged as against a proposed act of Parliament that it will be unconstitutional because in violation of the general principles and usages recognized by the unwritten constitution. But when adopted the statute in practical effect modifies the constitution, and is fully operative and potent. In this country, however, a statute which is in violation of the constitution is wholly invalid and impotent, and the constitution remains unaffected.