The process of legal evolution is threefold. It comprises in the first place the increase or growth of law—that is to say, the substitution of legal principles for the discretion of courts, and the transformation of fact into law. It involves in the second place the opposite process of the decrease of law—the reconquest by the arbitrium judicis of domains formerly occupied by legal principle—the transformation of law into fact. Finally it includes the alteration of law—that is to say, the destruction of one legal principle and the substitution of another in its stead.
To carry out this threefold process, it is clear that we require instruments of legal development which are capable not merely of creating new law, but of destroying old. It is not sufficient to obtain new law which stands side by side with the old, as a supplement to it; it is necessary to obtain new law which excludes the old, as a substitute for it. We must possess instruments of abrogative, and not merely instruments of constitutive power. So far we have considered the sources of law only in respect of this latter operation. We have yet to consider to what extent they possess the power of destroying law, as well as of creating it. The conservative virtue of the law has at all times been very great. We find, accordingly, that the constitutive operation of the sources is much more general than the abrogative. It by no means follows that, because a certain fact is capable of giving rise to a new rule, it is equally capable of getting rid of an old one. Legislation, indeed, is pre-eminent in this respect above all other legal sources. Alone among the instruments of legal development, it works with equal facility in both ways; and it is this peculiarity which makes it so efficient a method of legal reform.
In the strict theory of the law, precedent is wholly constitutive, being quite destitute of abrogative power. When the law is already settled, the judges have no authority save to obey and administer it. Their power of making new law by way of judicial decision is limited to those vacant spaces where there is as yet no other law which they can apply. Precedents make law, but cannot alter it.
Mercantile custom resembles precedent. So long as the ground is vacant—so long as there is no rule of the common law in pari materia—the proved custom of merchants will be allowed by the courts as a source of new law. But so soon as from this or any other source principles have been once established in the matter, there is no longer any room for new rules thus arising. Immemorial custom, on the other hand, has full power to derogate from the common law, though the statute law is beyond its operation.
Agreement possesses considerable, though not complete, abrogative power. A great part of the law is subject to supersession and modification by the consent of all persons interested. Modus et conventio vincunt legem. It is law only until and unless there is some agreement to the contrary. The residue of the law, however, is peremptory, and not to be thus excluded by consent. Agreements which attempt to derogate from it, and to establish special law in place of it, are illegal and void.
§ 48. Sources of Law and Sources of Rights.
The sources of law may also serve as sources of rights. By a source or title of rights is meant some fact which is legally constitutive of rights. It is the de facto antecedent of a legal right just as a source of law is the de facto antecedent of a legal principle. An examination of any legal system will show that to a large extent the same classes of facts which operate as sources of law operate as sources of rights also. The two kinds of sources form intersecting circles. Some facts create law but not rights; some create rights but not law; some create both at once. An act of Parliament for example is a typical source of law; but there are numerous private acts which are clearly titles of legal rights. Such is an act of divorce, or an act granting a pension for public services, or an act incorporating a company. So in the case of precedent, the judicial decision is a source of rights as between the parties to it, though a source of law as regards the world at large. Regarded as creative of rights, it is called a judgment; regarded as creative of law, it is called a precedent. So also immemorial custom does upon occasion give rise to rights as well as to law. In respect of the former operation, it is specifically distinguished as prescription, while as a source of law it retains the generic title of custom. That an agreement operates as a source of rights is a fact too familiar to require illustration. The proposition which really needs emphatic statement in this case is that agreement is not exclusively a title of rights, but is also operative as a source of law.
§ 49. Ultimate Legal Principles.
All rules of law have historical sources. As a matter of fact and history they have their origin somewhere, though we may not know what it is. But not all of them have legal sources. Were this so, it would be necessary for the law to proceed ad infinitum in tracing the descent of its principles. It is requisite that the law should postulate one or more first causes, whose operation is ultimate, and whose authority is underived. In other words there must be found in every legal system certain ultimate principles, from which all others are derived, but which are themselves self-existent. Before there can be any talk of legal sources, there must be already in existence some law which establishes them and gives them their authority. The rule that a man may not ride a bicycle on the footpath may have its source in the by-laws of a municipal council; the rule that these by-laws have the force of law has its source in an act of Parliament. But whence comes the rule that acts of Parliament have the force of law? This is legally ultimate; its source is historical only, not legal. The historians of the constitution know its origin, but lawyers must accept it as self-existent. It is the law because it is the law, and for no other reason that it is possible for the law itself to take notice of. No statute can confer this power upon Parliament, for this would be to assume and act on the very power that is to be conferred. So also the rule that judicial decisions have the force of law is legally ultimate and underived. No statute lays it down. It is certainly recognised by many precedents, but no precedent can confer authority upon precedent. It must first possess authority before it can confer it.
If we inquire as to the number of these ultimate principles, the answer is that a legal system is free to recognise any number of them, but is not bound to recognise more than one. From any one ultimate legal source it is possible for the whole law to be derived, but one such there must be. A statute for example may at any time give statutory authority to the operation of precedent,[[109]] and so reduce it from an ultimate to a derivative source of law.[[110]]