The Constitutional Court lists five requirements for customary constitutional law to arise, all of which are requirements for customary law in general. On a basic constitutional matter, a practice or precedent must exist; it must be repeated or continued long enough that the people recognize it and accept that it will not disappear; it must be constant, with no contrary practice arising along the way; and it must be clear rather than vague enough to allow several interpretations. In addition, the practice must win the people's approval or conviction, a broad consensus, as a constitutional custom, so that the people believe it is binding. Elaborating on this last requirement, the Court says it is enough that the people generally regard the practice as having become valid law, without needing to reach the level of legal conviction. The first four may be seen as objective requirements and the last as a subjective one. In the end, the Court names three requirements: a matter reserved to the constitution, the objective requirements of customary law, and the subjective requirement of customary law.

The subjective requirement needs further explanation. It has been pointed out that, for the question of whether Seoul's status as capital is customary constitutional law, the subjective requirement must be judged with more care than usual. A custom or practice normally involves the repetition of certain acts, but there is no such repeated act in the question of moving the capital; what is at issue is only the single fact or situation that Seoul has long been the capital. Where an external fact independent of any actor is at issue, the subjective element can be divided into three stages: accepting the fact as a fact; being conscious of the fact as something that ought to be, though not yet as law; and recognizing the continuation of the fact as law. In an ordinary practice, by contrast, performing the act already expresses a sense of obligation. So if people take it for granted that Seoul is the capital, one must ask whether they accept it merely as a fact or as a normative proposition.

It is also hard to tell whether such an 'ought' is a legal norm. Even if the idea that Seoul should be the capital is widespread, if it results from policy considerations, that alone would not make it customary constitutional law. For ordinary customary law, legal recognition can be found when people generally feel that acting against the custom breaches a legal duty. But when a constitutional custom is changed by legal measures, as with moving the capital, this does not appear as a sense of illegality; there is only an awareness that an old rule in the form of custom is being replaced by a new written law.

Note: On October 21, 2004, the Constitutional Court ruled 8 to 1 that the Special Act on the Construction of a New Administrative Capital was unconstitutional because it changed the customary constitutional rule that Seoul is the capital by statute rather than by amendment, infringing the right to vote in a constitutional referendum (2004Hun-Ma554). On November 24, 2005, it dismissed challenges to the later special act on a multifunctional administrative city, finding that the city would not become the capital and Seoul's capital functions would not be dismantled (2005Hun-Ma579), and Sejong Special Self-Governing City was launched on July 1, 2012.