The binding legal force of customs is based on the proposition longa et invetarata consuetudo, opinio necessitates. In other words, something that happens continuously over a long period of time will give rise to the assumption that it is something important.

Frequentia actus multum operator which means repeated actions will Custom or habit must be distinguished from habit, even though in the Indonesian vocabulary, both custom and habit are interpreted as habits. Habit is defined as an action that is carried out without any connection with an obligation or necessity to do so. This is different from the habits described above.

Meanwhile, convention is basically customary law in legal practice and order that has existed for a long time and continuously.

Custom is an independent source of law and is recognized by law. A number of articles in the Civil Code recognize customary law as a source of law. Article 1339 of the Civil Code states, "An agreement is not only binding for the things stipulated therein, but also for everything which, according to the nature of the agreement, is required by propriety, custom or law". Likewise, Article 1347 of the Civil Code reads, "Things which according to custom are forever agreed upon are included in the agreement, even if not expressly stated."