The interpretation of law is a complex matter. In the United Kingdom, the desideratum in regard to statutory interpretation is for the courts to discern Parliament's intent. The House of Lords in Maunsell v. Olins ( A.C. 373) approved a "unified contextual approach" (a la Cross) that prioritizes a contextually sensitive but literal reading of the words of the relevant act. Since Pepper v. Hart ( AC 593), courts may (but are not obliged to) consult Hansard (the edited record of what has been said in Parliament, including votes, written ministerial statements, and written answers to parliamentary questions) to assist them in discerning parliamentary intent, a procedure previously not permitted. The proper interpretation of case law is notoriously difficult even though here no question of discerning legislative intent arises. Constitutional interpretation is no less complex. A lively debate on the appropriate method or methods of constitutional interpretation is taking place, particularly in jurisdictions with a written constitution. In the Anglophone world, the United States is the locus of the most interesting and active debate.
There are two basic approaches to constitutional interpretation: originalism, which makes the intention of the drafters, the intention of the approvers, or the meaning of the text as it was understood or would have been understood by the drafters or approvers the criterion of interpretation; and vitalism, which prioritizes the needs of contemporary society over any strict intentional or semantic textual construction.
Vitalists, who believe that original intent, meaning, or understanding is either unobtainable or, if obtainable, cannot be allowed to constrain the courts' hermeneutic practice, typically want a constitution to be construed as a living document.
Originalism comes in two basic varieties that are often conflated--original intent and original meaning (sometimes called original understanding). Original intent is not an easy position to defend (despite the norm of statutory interpretation being the discernment of Parliament's intent) for the simple reason that it is difficult, if not impossible, to comprehend anyone's intent even here and now, let alone what it was seventy or two hundred years ago. When originalism is summarily dismissed, it is usually original intent that is being rejected. Original meaning (or understanding), however, is a matter of historical investigation and is no more or no less difficult to ascertain than any other matter of historical investigation. Interpretations based on this criterion may not be rationally coercive, but they are rational.
Vitalism, in contrast, appears to undermine the very point of having a constitution in the first place, allowing constitutional interpretation to become a kind of rhapsodic free association only tangentially connected to the constitutional text. The purpose of such interpretation often appears to be to explain away the text rather than to explain it. (See Keith Whittington's  devastating critique of theories of textual indeterminacy, such as deconstruction, structuralism, poststructuralism, reader-response theory, and hermeneutics, all of which are frequently--but mistakenly--taken to render all forms of originalism otiose.)
I do not pursue these topics further here. (Interested readers may consult Casey 2004, 2005, and 2009 and their associated bibliographies.) My reason for bracketing these matters is simply that the whole debate on constitutional interpretation, fascinating as it may be, takes place under the umbrella of a prior assumption--namely, that constitutions, howsoever they may be interpreted, are authoritative. Why should we believe they are?
What Are Constitutions? How Do They Come into Being? Why Are They Authoritative?
A constitution is a document, a set of documents, or, in the case of the United Kingdom, a mixture of legislation, case law, conventions, and customs that is considered to be the basic law of the state. The distinction between written and unwritten constitutions should not be exaggerated. As Hilaire Barnett notes, "Under all constitutions, not all of the rules will be written, and still less will they be collected within a single document" (1998, 3). A constitution generally sets out the structure of the organs of government, orders their relationships to each other and to the state's citizens, and may include a bill of rights or similarly functioning provisions, either integrally as a series of amendments or as an act of Parliament (Parpworth 2000, 3).
Constitutions being what they are, how does a state acquire one? The answer varies depending on the state. In the United Kingdom, the Constitution is largely a creature of its eventful political history, and the Constitution of the United States of America is the product of a postrevolutionary constitutional convention (intended originally merely to revise the Articles of Confederation), whereas the Irish Constitution is a creation of the executive branch of government, as approved by the Dail (Irish Parliament) and ratified by plebiscite (about which I write more later).
So far, matters are relatively uncontroversial. However, the really important question about constitutions is not what they are or how states come to acquire them, but why they are supposed to have the authority that most people appear to grant them. Is a constitution a contract subsisting between the state's citizens, some other kind of noncontractual agreement, or something completely sui generis? The possibilities would seem to be either (a) that a constitution is a binding agreement among a group of people to be governed in a particular way or (b) that it is binding but not the subject of an agreement. (The other two possibilities are that it is a nonbinding agreement or a nonbinding nonagreement--the latter is so close to being nothing that it makes no difference, and the former, though possible, could hardly function as a fundamental law.) flit is a binding agreement, there are two subpossibilities--it is either explicit or implicit.
Is a Constitution a Contract?
It is not unusual for constitution makers to represent the objects of their constructive activities as compacts, covenants, or contracts. The preamble of the Massachusetts Constitution of 1780 claims that "[t]he body-politic is formed by a voluntary association of individuals: It is a social compact, by which the whole people covenants with each citizen, and each citizen with the whole people, that all shall be governed by certain laws for the common good" (in Handlin and Handlin 1966, 441).
The paradigm of the binding agreement is the contract. The standard view of a contract is that the agreement that forms its substance requires a valid offer and a valid acceptance of that offer, and, despite challenges (from Lord Denning--who else?), this view would still appear to be the received one. The agreement may be bilateral (an exchange of promises) or unilateral (where the offeror alone makes a promise, the acceptance of which consists in someone's doing what is set out in the offer). To be valid, an offer must be communicated. The communication may be in writing, speech, or conduct, but in any event it must be definite, and it must be distinguished from a mere invitation to treat. To be valid, the acceptance of an offer must be made while the offer is still operative, must be made by the offeree (if bilateral), must match the terms of the offer, and may be written, oral, or inferred from conduct. Of course, the acceptance must be communicated to the offeror.
In addition to its offer-acceptance structure, a contract in the Anglo-American legal tradition also requires that something in the arrangements indicate that the promisor intends to be bound by the agreement. So, for example, a properly constituted deed will be one such arrangement; if one were to believe Lord Denning, promissory estoppel would be another. But these special cases to one side, consideration is the standard "badge of enforceability," where consideration is defined as "some right, interest, profit or benefit to one party" or "some forbearance, detriment, loss or responsibility given, suffered or undertaken by the other" (Currie v. Misa  LR10 Ex 153).
In general, the doctrine of privity dictates that only the parties to a contact can sue or be sued on a contract. There are exceptions to this doctrine in regard to the assignment of rights, in the matter of agency, in trusts and multipartite agreements, and in some aspects of land law (restrictive covenants), and there are some statutory exceptions. Third parties can enforce a contractual provision of benefit to them where the contract expressly provides for third-party benefit or where the contract is intended to provide third parties with legally enforceable rights. However, I know of no case in which third parties (other than, say, principals in a principal-agent relationship) may be burdened by a contract to which they are not explicitly a party.
If the constitution is to be construed as a contract, we might well wonder what the offer is, what would constitute acceptance, who is (are) the offeror(s), who is (are) the offeree(s), what was the consideration, and, finally, who is included in the privity of the contract.
The Constitution as an Explicit Contract
Despite these difficulties, some observers can conceive of a constitution only as a contract. Lysander Spooner (1808-87), an American lawyer, entrepreneur, abolitionist, and protolibertarian, is one such. He has no doubt that the U.S. Constitution purports to be a contract. "It has no authority or...