Canon 1507

1. Only that custom can have the force of law which is reasonable and introduced by a community capable at least of receiving law, and has been the continuous and uncontested practice

for the prescribed time determined by law. 2. A custom which

is expressly reprobated in law is not a reasonable one. 3. A

custom contrary to the current canon law or one which is apart

(praeter legem) from canon law, obtains the force of law only

when it has been legitimately observed for thirty continuous and

complete years; only a centenary or immemorial custom can prevail

over a canon which contains a clause forbidding future customs.

4. Even before that time, a competent legislator can approve a

custom as legitimate by his consent, even tacitly.