Originally uploaded at SSRN.


Real property can only be held and conveyed in a small number of forms, such as fee simple, life estate, and lease. This principle is known as numerus clausus, meaning “the number is closed.” For centuries, the principle has been central to the common-law system of property rights. Scholars have justified it as a mechanism for facilitating effective property alienation, maintaining low transaction costs in the buying and selling of property, and keeping the scope of property owners’ rights clear.

In contrast, the numerus clausus principle is essentially nonexistent in intellectual property law. In the context of patents and copyrights, “the number is open.” There is nearly no limit to the ways in which intellectual objects can be licensed and sold.

This Article will argue that the numerus clausus principle should extend to intellectual property. The justifications for the numerus clausus principle in real property law are even more persuasive in the intellectual property context because the scope of intellectual property rights is more difficult to delineate than the scope of real property rights. The metaphysical nature of intellectual property prevents protected objects from being clearly identifiable, particularly in a patent context, where inventions can be independently created by multiple parties.

As a result, investigating the sale and licensing history of a work or invention — and whether a work or invention is protected at all — is difficult, costly, and sometimes impossible. This difficulty is compounded by the absence of numerus clausus, which permits inscrutable licensing and sale agreements and allows single works to be carved into several parts and burdened by complicated usage rules.

By considering examples of digital content licensing and fragmentation of particular copyrights, this Article will identify how a numerus clausus principle for intellectual property would facilitate the use and conveyance of intellectual property. This principle would benefit intellectual property owners, licensees, and the general public by lowering transaction costs and preventing accidental overuse and underuse of intellectual works.