SUCH is the custom of gavelkind in Kent and some other parts of the kingdom (though perhaps it was also general till the Norman conquest) which ordains, among other things, that not the eldest son only of the father shall succeed to his inheritance, but all the sons alike: and that, though the ancestor be attainted and hanged, yet the heir shall succeed to his estate, without any escheat to the lord.--Such is the custom that prevails in divers antient boroughs, and therefore called borough-english, that the youngest son shall inherit the estate, in preference to all his elder brothers.--Such is the custom in other boroughs that a widow shall be intitled, for her dower, to all her husband's lands; whereas at the common law she shall be endowed of one third part only.--Such also are the special and particular customs of manors, of which every one has more or less, and which bind all the copyhold-tenants that hold of the said manors.--Such likewise is the custom of holding divers inferior courts, with power of trying causes, in cities and trading towns; the right of holding which, when no royal grant can be shewn, depends entirely upon immemorial and established usage.--Such, lastly, are many particular customs within the city of London, with regard to trade, apprentices, widows, orphans, and a variety of other matters; which are all contrary to the general law of the land, and are good only by special custom, though those of London are also confirmed by act of parliament[a]. [Footnote a: 8 Rep. 126. Cro. Car. 347.] TO this head may most properly be referred a particular system of customs used only among one set of the king's subjects, called the custom of merchants or _lex mercatoria_; which, however different from the common law, is allowed for the benefit of trade, to be of the utmost validity in all commercial transactions; the maxim of law being, that "_cuilibet in sua arte credendum est_." THE rules relating to particular customs regard either the proof of their existence; their legality when proved; or their usual method of allowance. And first we will consider the rules of proof. AS to gavelkind, and borough-english, the law takes particular notice of them[b], and there is no occasion to prove that such customs actually exist, but only that the lands in question are subject thereto. All other private customs must be particularly pleaded[c], and as well the existence of such customs must be shewn, as that the thing in dispute is within the custom alleged. The trial in both cases (both to shew the existence of the custom, as, "that in the manor of Dale lands shall descend only to the heirs male, and never to the heirs female;" and also to shew that the lands in question are within that manor) is by a jury of twelve men, and not by the judges, except the same particular custom has been before tried, determined, and recorded in the same court[d]. [Footnote b: Co. Litt. 175 _b._] [Footnote c: Litt. Sec. 265.]