The rule, therefore, that a particular custom is invalid unless immemorial means in practice this: that if he who disputes its validity can prove its non-existence at any time between the present day and the twelfth century, it will not receive legal recognition. It is not necessary for the upholder of it to prove affirmatively its existence during the whole of that period. If he can prove that it has existed for a moderate period, say twenty years, from the present day, this will raise a presumption of its immemorial antiquity, which must be rebutted by him who disputes it.[[135]]
It is not difficult to understand the reason which induced the law to impose this stringent limitation upon the efficacy of local customs. It was designed in the interests of a uniform system of common law for the whole realm. Had all manner of usages been recognised without any such limitation, as having the force of special law, the establishment and maintenance of a system of common law would have been rendered all but impossible. Customary laws and customary rights, infinitely various and divergent, would have grown up so luxuriantly, as to have choked that uniform system of law and rights which it was the purpose of the royal courts of justice to establish throughout the realm.[[136]]
Origin of the rule as to time of memory.—The requirement of immemorial antiquity was introduced into the English law courts of the twelfth or thirteenth century from the canon law. In two respects the Canonists developed and rendered more definite the somewhat vague and indeterminate theory of customary law which we find in the writings of the Roman lawyers. In the first place, clear recognition was accorded to the distinction between jus commune and consuetudines, the former being the common, general, or written law of the whole Church, while the latter consisted of the divergent local and personal customs which were added to, or substituted for the jus commune in particular places or in respect of particular persons. This nomenclature, with the conceptions expressed by it, passed from the canon law to the law of England.
In the second place the Canonists attempted to supply a defect of the civil law by laying down a fixed rule as to the necessary duration of customs. They determined that no consuetudo was to be held valid, so as to derogate from the jus commune, unless it was praescripta, that is to say, unless it had endured during the legal period of prescription. Consuetudo praescripta praejudicat juri communi.[[137]]
What, then, was the period of prescription thus required? On this point we find no agreement among the doctors, for there were several different forms of prescription known to Roman law, and there was no unanimity among the Canonists in the selection of any one of them as a test of the validity of custom. Many favoured the adoption of the ordinary decennial prescription of Roman land law, and held that a custom must have endured for ten years at least, but need have lasted no longer.[[138]] Others demanded forty years, since this is the prescription required as against the Church by the legislation of Justinian.[[139]] At one time, however, there was a widely held opinion that the true time of prescription required to enable a custom to derogate from the common law of the Church was time immemorial. Illa consuetudo praejudicat juri, cuius non exstat memoria hominum.[[140]]
This conception of time of memory as a period of prescription was derived from the civil law. Immemorial prescription was there a mode of acquiring servitudes. Ductus aquae cuius origo memoriam excessit, jure constituti loco habetur.[[141]] The Canon law adopted this rule, and made a more extensive use of it. Immemorial prescription became a supplementary mode of acquisition, available in all cases in which there was no shorter period of prescription to which a claimant might have recourse. From the canon law it passed into the laws of France, Germany, and England.[[142]]
As already stated, then, many Canonists recognised time immemorial not merely as a period of prescription, but as a condition of the validity of customary law. Suarez, writing at the end of the sixteenth century, tells us, indeed, in the course of an exhaustive examination of the theory of customary law, that in his day this doctrine was no longer received.[[143]] Long before Suarez, however, it had established for itself a secure place in the law of England. The canonical principles of consuetudo rationabilis et praescripta and of tempus immemoriale were in the thirteenth century at the latest incorporated in our legal system by those ecclesiastical lawyers who laid the foundations of it. This, indeed, was the only form of prescription which obtained recognition from the common law. We find the rule settled with perfect definiteness in the earliest Year Books of Edward I.[[144]]
5. Conformity with the common law.—The fifth and last requirement of a valid custom is that, unless immemorial, it must be consistent with the common law. That it must be consistent with statute law is, as we have already seen, a rule applicable to all customs whatever, whether immemorial or not. That it must be consistent with the common law is a rule applicable only to recent customs, and not to those which have the prestige and authority of immemorial antiquity. Modern custom possesses constitutive, but no abrogative power; it must operate in the spaces left vacant by the law already established; it may supplement the law, but cannot derogate from it. Immemorial custom, on the other hand, can destroy as well as create, so far as the common law is concerned; though as against the statute law it is as powerless as the most ephemeral usage.[[145]]
The combined effect of the various rules which we have considered is to render custom less and less important as a source of new law. As the legal system develops, the sphere within which custom is operative grows gradually smaller. For, in the first place, custom cannot derogate from statute law, and this latter tends progressively to absorb into itself the whole of the common law. In the second place, the requirement of immemorial antiquity precludes local custom from operating as an instrument of fresh legal growth. Such customs may now be proved and applied for the first time, but they cannot now for the first time come into existence. In the third place, all recent custom must be consistent with the law as already established, whether common or statutory. As the law develops and completes itself, therefore, there is less and less room left for the constitutive operation of custom. There are fewer vacancies within which customary law may grow. It is for this reason that the growth of general customary law has already all but ceased. Until a comparatively recent date, a great part of mercantile law was so imperfectly developed as to leave very considerable scope for the operation of mercantile custom. The law as to negotiable instruments, for example, was chiefly customary law. But at the present day our mercantile law is so complete that it is only in comparatively rare cases that the custom of merchants has any opportunity of serving as the ground of new principles.