The Subsidiary Sources

3. Customs

Customs are social habits, patterns of behaviour, which all societies evolve. In a sense custom should be accorded as one of the principal sources of law for much, if not most, law was originally based upon it. Moreover custom is not solely important as a source of law, for even today some customary rules are observed in their own right and they command almost as much obedience as rules of law proper; they only differ from rules of law in that their observance is not enforced by the organs of the State. Thus, it will be seen that many of the fundamental rules governing the Constitution are 'conventional' (i.e. customary), rather than legal, rules.

But in modern times most general customs (i.e. customs universally observed throughout the realm) have either fallen into desuetude or become absorbed in rules of law. For example many of the early rules of the common law were general customs which the courts adopted, and by this very act of adoption made into law. So too, much of the modern mercantile law owes its origin to the general customs of merchants which the courts assimilated. So also many of the rules of the law relating to the sale of goods originated as customs, were adopted by the courts, and eventually moulded into a statutory code. General custom has therefore now ceased to operate as an important source of law. For law, whether enacted or judicially declared, has in most fields superseded custom.

4. Books of authority

On the Continent the writings of legal authors form an important source of law. In England, in accordance with the tradition that the law is to be sought in judicial decisions, their writings have in the past been treated with comparatively little respect. They have been cited in court, if citied at all, rather by way of evidence of what the law is that as independent sources from which it may be derived.

This general rule has, however, always been subject to certain recognized exceptions; for there are certain ‘books of authority’, written by authors of outstanding eminence, which may not only be cited as independent sources in themselves for the law of their times but which also carry a weight of authority almost equal to that of precedents.

In modern times the established tradition appears to have been breaking down, because many textbooks are now in practice constantly cited in the courts, though only the best of them are likely to command attention. The reason for this departure from the established tradition is probably that in comparatively recent years a large increase in the popularity of the study of English law in all our major universities has done much to improve the quality of legal writing and to increase the volume of legal literature. Thus, today books of authority are commonly referred to in court and even works of living authors are now often cited, though by a rule of etiquette, counsel who refers to works of the latter category should not cite them directly as authorities, but should request the leave of the court to ‘adopt’ the arguments which they contain as part of his own submissions. In practice, however, even this latter etiquette is now not always observed.