Customary law

Customary law (관습법/慣習法) is customs in law that can be objectively verified within a particular social setting. It should be positively in defense of "what has always been done and accepted by law."

Customary law is to be exits when:
 * a certain legal practice is observed and
 * the relevant actors consider it to be law (opinio juris).

The term customary law can also apply to areas of international law where certain standards have been nearly universal in their acceptance as correct bases of action - in example, laws against piracy or slavery (see hostis humani generis). In many, though not all instances, customary laws will have supportive court rulings and case law that has evolved over time to give additional weight to their rule as law and also to demonstrate the trajectory of evolution (if any) in the interpretation of such law by relevant courts.

Customary law and codification
Customs amd practices observed repetitively for a long time and largely in communities have developed into law with a sense of law unless they conform with public policy, or social order and good customs (사회질서와 선량한 풍속).

The modern codification of civil law developed from the tradition of time-honored customaries, collections of customary law that developed in particular communities, slowly gathered, and later written down by local jurists. Customaries acquired the force of law when they became the undisputed rule by which certain rights, entitlements, and obligations were regulated between members of a community.

Instances
Under the Civil Act, if there is no provision in laws applicable to certain civil affairs, ustomary law shall apply, and if there is no applicable customary law, sound reasoning (조리/條理) shall apply. Article 1. (Source of Law)

The customary law is acknowledged in case of:
 * Explicit ownership demonstration method (명인방법/明認方法)
 * Legal superficies in customs (관습상의 법정지상권/慣習上 法定地上權). See below.
 * Tomb base land right (분묘기지권/墳墓基地權)
 * Title trust (명의신탁/名義信託)
 * Yangdo dambo or fiduciary transfer of title (양도담보/讓渡擔保)
 * de facto Marriage (사실혼/事實婚), etc.

Legal superfices in customary law
Take an example of the legal land use right (surfices) under customary law (관습법상 법정지상권/慣習法上法定地上權). Suppose the ownership of a land and a building both of which originally belonged to one person has been separated on other accounts than the Civil Act or other statutes. Then the court acknowledges that the new owner of the building has acquired the superfices.

The Supreme Court ruled:
 * "원래 관습에 의한 지상권을 인정한 취지는 건물과 토지를 별개의 물건으로서 취급하고 있는 우리 법체제 하에서는 건물과 그 건물이 서 있는 토지는 항상 별개의 물건으로 거래되고 있으나, 실지에 있어서 건물은 그 성질상 그 토지의 이용 없이는 건물로서의 이용을 할 수 없는 것이므로, 같은 소유자의 소유에 속하였던 건물과 그 대지 중 어느 하나가 매매 등으로 그 소유자를 달리한 때에는 다른 특별한 사정이 없는 한, 건물소유자로 하여금 대지에 대하여 지상권을 취득한 것으로 봄으로써, 그 건물로 하여금 건물로서의 가치를 유지케 하자는 국민경제상의 필요에 의하여 인정한 제도라 할 것이다."