The best known part of the numerus clausus is the limited number of forms. In many civil jurisdictions, this may result in a suboptimal number of forms of ownership.17 Customs can be complementary, but as we describe below, we expect customs that make the right information trade-offs are more likely to be recognized as new forms of ownership. . In this essay, we define both the principle of the „strict“ numerus clausus and the „strict“ numerus-apertus principle narrowly. The former means that only laws can create new forms, while the latter means that anyone can create new forms of property through contracts. This non-mutually exclusive way of defining these two terms leaves much room for what we call the „middle approach,“ such as laws and customs sanctioned by the courts as duopolistic creators of new forms of property. If either term were to be broadened to cover the bulk of incidents, we should think it should be numerus clausus: intermediate systems usually contain a presumption against new forms and a safety valve for the creation of new ones. Indeed, it could be argued that all systems – including those with a numerus apertus – contain at least one implicit presumption against new forms and often an explicit restriction on them (e.g. registration or registration with formalities to obtain effect with third parties). .
Our theory of optimal standardization does not explain the origin of the numerus clausus principle, but provides an economic basis for its usefulness and explains why it persists when the political reasons that motivated this principle no longer exist. It should also be noted that numerus clausus literally means „the number is closed“, but in civil law it contains an equally important connotation: the number is closed unless the legislator enacts new forms. In other words, the legislator can always increase or decrease the number of types of ownership forms, or the legislator can change the content of any form. According to the traditional understanding of this principle, no other institution (including the courts) can create or modify new forms. Therefore, the boundary between customary forms of property and legal interests is clear: only forms of property promulgated by the legislature (in civil codes or special laws) are legal; A widespread form sanctioned by the courts, but not found in books, can only be common. Since 2009, when the Taiwanese Civil Code was amended, Taiwanese courts have not explicitly recognized a new form of customary law.  Nevertheless, Taiwanese courts in the second half of the twentieth century recognized several new common forms of property without discussing the principle of numerus clausus. In the first subsection, we discuss two common security interests.
The second subsection describes an interest of use akin to ownership – the de facto right of disposal. This subsection explains another example, the „de facto right of disposition“126 of illegal buildings where the courts have done all the work on their own. We use this example to illustrate once again our thesis that courts are likely to recognize customs, impose low information costs on third parties and create high value, although this violates the principle of numerus clausus. . The Chinese government also faces the thorny problem of „small real estate.“ Small properties are illegal and therefore cannot be registered, yet they are bought and sold in very large quantities. See Shitong Qiao, Small Property, Adverse Possession, Optional Law, and „Small Property“, in Law and Economics of Possession, op. cit. cit., note 73, p. 290 (describes the dilemma facing local governments in China: „Demolition [of small plots] proved impossible; their legalization would encourage more illegal constructions“); see also Shitong Qiao & Frank Upham, Relational Property and the Evolution of Property Rights: A Case of Chinese Rural Land Reform, 100 Iowa L. Rev. 2479, 2495 (2015). .
It is questionable whether the usual property rights in Korea and elsewhere resolve the „fixed content“ part or the „limited number“ part of the numerus clausus principle. As explained in note 15 above, this is not as important in terms of optimal standardization theory, although courts are more likely to be willing to change the content of existing forms rather than create new ones for reasons of information costs. In the final part of this essay, a case study on Taiwan shows that courts are willing to overcome the numerus clausus principle and recognize customs when the cost of information is low and the benefits of new forms are high. Since the 1950s, many buildings in Taiwan have been constructed without permission and therefore could not be registered in the official real estate registry. However, according to Taiwanese Civil Code (Article 758), property and other property rights may be transferred de jure only if they are registered. These „illegal constructions“ were already being traded in large numbers.21 The courts could rule that no property rights were legally transferred; Instead, through a series of precedents, Taiwan`s Supreme Court has repeatedly ruled that while ownership does not change hands, buyers acquired a „de facto right of disposition,“ which, of course, does not exist in the Civil Code. Between 1918 and the 1950s, a number of private universities and medical schools in the United States instituted numerus clausus guidelines that prohibited the admission of students based on their religion. or the race for certain percentages in the United States. College population.
Many minority groups have been negatively affected by these policies; One of the affected groups were Jewish applicants, whose admission to some liberal arts colleges in New England and New York declined significantly between the late 1910s and mid-1930s.  For example, the admission rate increased from 27.6% to 17.1% at Harvard University during this period, and from 32.7% to 14.6% at Columbia University. Corresponding quotas were introduced in medical and dental schools, resulting in a decline in the number of Jewish students in the 1930s: for example, at Cornell University Medical School from 40% in 1918-22 to 3.57% in 1940-41, at Boston University School of Medicine from 48.4% in 1929-30 to 12.5% in 1934-35. At Yale University, Dean Milton Winternitz`s instructions to the admissions office regarding ethnic quotas were very specific: „Never admit more than five Jews, take only two Italian Catholics, and take no blacks at all.“  During this period, a notable exception among American medical schools was the Middlesex University School of Medicine, which had no quotas, and many Jewish faculty members and students; School officials believed anti-Semitism played a role in the school`s denial of AMA accreditation.  The admission of customary law as a source of law is often the first step towards relaxing the numerus clausus. Ownership forms that are not on the approved finished list are not supposed to be allowed under the classic numerus clausus, yet in some systems custom seems to be able to expand the list in some cases. If a court recognizes a use of property, this contradicts the institutional choice of the numerus clausus: the classical principle reserves changes in the menu of property rights to the legislator.61 Under this classic approach, courts should refrain from recognizing new forms of property, and yet generous recourse to customary law is a means of making legislative changes over judicial changes in the field of fundamental property rights.61 circumventing property rights. The universities of French-speaking Western Switzerland have not decided to introduce a numerus clausus.
Instead, these universities offer unlimited access to the first-year medical program; And the best first-year students are allowed to continue their medical studies at the same university or another. Other popular faculties such as psychology or journalism also have aptitude tests – but they only concern one university. . The de facto right of disposition is a close or substitute for property and may therefore not be the new forms of property that proponents of the numerus clausus principle and the numerus-apertus principle have in mind. The extent to which the numerus apertus principle imposes external information costs on third parties depends on how the numerus apertus principle is legally implemented. In other words, is the numerus-apertus principle different from the numerus-clausus principle? Or is the numerus-apertus principle simply the antithesis of the numerus-clausus principle with other institutional agreements between them? In the context of civil law, the principle of numerus clausus can be translated, since only laws can create new forms of property.