Should the number of ways to transfer intellectual property rights be limited? Real property may only be held in certain standardized forms (fee simple, lease, etc.), a principle first termed "numerus clausus" ("the number is closed") by Merrill & Smith in a 2000 Yale Law Journal article. "The justifications for the numerus clausus principle in real property law are even stronger in the intellectual property context," argues Christina Mulligan (Yale Law School Information Society Project) in her forthcoming article, A Numerus Clausus Principle for Intellectual Property.
Mulligan reviews the use of numerus clausus in real property and groups the theoretical justifications for these restraints into three categories: (1) facilitating the alienation of property; (2) lowering third-party information costs (by making it easier to determine how property is held); and (3) making it easier for parties with an interest in the property to understand and verify their ownership rights. She then argues that the effects of a lack of numerus clausus—"significant restraints on the alienation of property, increased transaction costs of property conveyance, and confusion over the scope of property rights"—are "visibly present in intellectual property law."
One of Mulligan's examples, Monsanto seed licenses, is particularly topical now that the Supreme Court has granted cert in Bowman v. Monsanto (considering whether patent exhaustion should apply to Monsanto's seeds). Other interesting examples include Microsoft software licenses preventing resale, a TV series being released on DVD with a new soundtrack due to failures in re-licensing the songs, a case of confusion when copyright to Betty Boop cartoons was separated from copyright to her character, and consumer uncertainty over rights to iTunes music.
So if you buy the argument that these are problems that could be addressed by numerus clausus in IP, what "forms" of IP should be allowed? Mulligan notes that too much standardization leads to its own problems, like frustrating the intent of contracting parties and loss of price discrimination, and that standardization should be required only in "pockets" of IP where its benefits outweigh its costs. For example, the arguments for numerus clausus seem less compelling in patent law, where contracting parties tend to be knowledgeable and the "comparatively short length of the patent term" makes excessive fragmentation of rights less likely. (Also, confusion about ownership might be more easily solved by a centralized patent license registry.)
In copyright law, however, unread shrinkwrap and clickwrap licenses are pervasive—as Mulligan notes, even Justice Roberts admits he does not read this fine print. She thus lays out the case for a digital first sale doctrine—under which digital works may be freely alienated as long as only one device is used to display or perform the work at a time—to "align rights in digital goods with existing consumer expectations." Mulligan also discusses possibilities such as exhaustion of derivative work rights (under which derivative rights may only be separated by contract, not as a matter of copyright) and indivisibility of all exclusive rights in a copyright.
Mulligan's work is a useful addition to a line of scholarship investigating the treatment of intellectual property as property—both in terms of where the analogy breaks down (e.g., Lemley's argument that the economic theories of real property do not apply to intellectual property) and where one field can learn from the other (e.g., Peter Lee's accession article). At the end of her article, Mulligan notes that the absence of numerus clausus in IP can also "teach us lessons about property law in general"; e.g., Texas developers argued that treating real property like copyright by requiring a cut of future resales would increase efficiency, but Mulligan argues that "the lesson from intellectual property is quite the opposite."