5. Customs ought to be certain. A cuſtom, that lands ſhall deſcend to the moſt worthy of the owner’s blood, is void; for how ſhall this worth be determined? but a cuſtom to deſcend to the next male of the blood, excluſive of females, is certain, and therefore good[1]. A cuſtom, to pay two pence an acre in lieu of tithes, is good; but to pay ſometimes two pence and ſometimes three pence, as the occupier of the land pleaſes, is bad for it’s uncertainty. Yet a cuſtom, to pay a year’s improved value for a fine on a copyhold eſtate, is good: though the value is a thing uncertain: for the value may at any time be aſcertained; and the maxim of law is, id certum eſt, quod certum reddi poteſt.
6. Customs, though eſtabliſhed by conſent, muſt be (when eſtabliſhed) compulſory; and not left to the option of every man, whether he will uſe them or no. Therefore a cuſtom, that all the inhabitants ſhall be rated toward the maintenance of a bridge, will be good; but a cuſtom, that every man is to contribute thereto at his own pleaſure, is idle and abſurd, and, indeed, no cuſtom at all.
7. Lastly, cuſtoms muſt be conſiſtent with each other: one cuſtom cannot be ſet up in oppoſition to another. For if both are really cuſtoms, then both are of equal antiquity, and both eſtabliſhed by mutual conſent: which to ſay of contradictory cuſtoms is abſurd. Therefore, if one man preſcribes that by cuſtom he has a right to have windows looking into another’s garden; the other cannot claim a right by cuſtom to ſtop up or obſtruct thoſe windows: for theſe two contradictory cuſtoms cannot both be good, nor both ſtand together. He ought rather to deny the exiſtence of the former cuſtom[2]
Next, as to the allowance of ſpecial cuſtoms. Cuſtoms, in derogation of the common law, muſt be conſtrued ſtrictly. Thus, by the cuſtom of gavelkind, an infant of fifteen years may by one
