The doctrine of waiver is referable to this maxim (See also Maxs. Nos. 216, 217 and 222.)
36. Constructio legis, non fecit injuriam. Construction of the law causes no injury.
* 37. Consuetudo ex certâ causa rationabili usitata privat communem legem. A custom based on a certain reasonable foundation obrogates the common law.
For example may be cited the custom of gavelkind, under which the land of a deceased person descended to all his sons equally, and the custom of Borough English, under which it descended alone to the youngest son. Both these customs supersede the common law of descent. (See Steph. Comm., Vol. I., and Maxs. Nos. 38, 153 and 197.)
38. Consuetudo pro lege servatur. Custom is protected by the law.
(See also Max. No. 37.)
39. Contemporanea exposito est optima et fortissima in lege. A contemporaneous interpretation is the best and strongest in law.
In interpreting an old document or statute, consideration must be had for the intention and intended effect at the time of its execution, on the ground that the same were then best known and appreciated. (See Chitty on Contracts, 16th ed. p. 95, and Max. No. 275.)
* 40. Contra non valentem agere nulla currit praescriptio. No prescription runs against one unable to act.
Generally, prescription runs only from the time when the plaintiff might have brought his action, unless then under disability. In actions brought to recover land, rent, or legacies, a certain additional time is allowed after the disability ceases. In actions having reference only to things strictly personal, the same time is allowed after the disability ceases, as would have been allowed at the time the cause of action accrued had no such disability then existed.