Property Law as a Programming Language Shrutarshi Basu James Grimmelmann Nate Foster Cornell University Cornell Law School Cornell University [email protected] [email protected] [email protected] Abstract of the formal languages programmers use to instruct computers Anglo-American law enables property owners to split up rights to in how to carry out computations. One of the great achievements a thing over time among multiple people by breaking their own- of the eld has been its development of elegant and rigorous ership apart into multiple future interests. e system of legal doc- semantics that use mathematical tools to explain what a given trines governing future interests is notorious among lawyers and program does and means. Here, we use those tools to describe the law students for its complexity. e conveyances property owners law of future interests. use to transfer and subdivide property rights follow rigid syntactic We do so by treating property conveyances as programs in a conventions and are governed by an intricate body of interlock- very restricted programming language. We show that the stan- ing legal doctrines that determine the legal eect of a conveyance dard terms used to describe and distinguish future interests can over time. ese doctrines have been codied, but only in infor- be represented using a formal syntax we call ConAbs. It has, for mal and potentially ambiguous ways. However, both the syntactic example, a specic representation for a life estate, a dierent rep- structure and underlying semantic of conveyances are amenable to resentation for a condition subsequent, and so on. We then give a analysis using tools and techniques from programming language precise semantics for ConAbs. is semantics is purely formal and theory and practice. is paper presents preliminary work in de- completely unambiguous: a given ConAbs representation always veloping a formal model for expressing and analyzing property behaves exactly the same way under the same circumstances. But conveyances. it captures the relevant legal doctrines, we think correctly. 2. Concepts and Terms 1. Introduction is section denes some concepts and terms that will be useful for Anglo-American property law governs what things can be owned, the rest of the paper. Property law deals with the rights of owners who owns them, what rights owners enjoy, and how these rights of property. For real estate, these rights are termed present estates can be transferred and divided. Some portions of property law, if their owner can currently excercise them, or future interests, if such as nuisance law (governing the relations among neighors) they can only be exercised (if at all) at some point in the future. We use open-ended standards and factually intensive balancing tests. will call any property right capable of being owned an interest. In- But other portions are infamous for their rigidity: they rely on terests are created (and the corresponding rights transferred) from intricate bright-line rules, and lots of them. one party (the grantor) to another (the grantee) in a variety of ways e most rigid, intricate, and bright-line portion of property (wills, deeds, etc.), which we will collectively call conveyances. law is the system of doctrines governing the division of ownership For a rst example, consider the simplest non-trivial con- of property over time. One can, for example, give ownership of veyance, shown in Conveyance 1. a tract of land to one person for her lifetime, and to another person thereaer. Although the system exhibits great exibility O conveys to A (1) in practice, that exibliity is achieved only by way of a dense O tangle of doctrines that restrict the permissible interests in a piece Here, assuming that started out owning the property out- A O of property. right, ends up owning it outright, because conveyed her en- A Frequently, lawyers, law students, and legal scholars regard tire interest to . e property term for this type of ownership is A these restrictive and rule-oriented portions of property law as fee simple absolute. is entitled to possess the property now and essentially arbitrary. Certainly, this is commonly how they are forever, and also to convey it to another grantee if he so desired. A taught: with a lot of rote memorization of denitions and exam- We will say that the nature of ’s interest is “possessory”, and that ples. Compared to the rest of property law, the law of future in- its duration is “fee simple absolute.” terests is regarded as excessively formal: full of fusty distinctions Now, consider the slightly more complicated example shown O A and traps for the unwary. in Conveyance 2. A grantor conveys an interest to a grantee A B Another way of thinking about the problem, though, is that not forever but for a shorter time: ’s lifetime. Aer that, is to A A perhaps this fragment of property law is not too formal but rather receive the property. Before ’s death, is entitled to possess and B not formal enough. e aempts to codify its doctines (most no- use the property; aerwards, is. tably in the 1936–40 Restatement of Property) went a long way toward making it precise, but they still rely on English descrip- O conveys to A for life, then to B (2) tions, and sometimes on highly ambigious descriptions. e un- is conveyance has two clauses (conventially separated by derlying rules, however, are oen well-dened enough that they commas) and it creates two distinct interests. A receives a life can support a genuinely rigorous formal treatment. estate and B receives a remainder in fee simple absolute. e nature In this paper, we give such a treatment, one that uses the tools of A’s interest is still possessory, but now its duration is something of programming language theory. is branch of computer science less than perpetual, it is a “life estate.” It will expire at A’s death. deals with the design, specication, analysis, and implementation B’s interest, on the other hand, has a dierent nature: it is called a “remainder”, because that is the name for an interest that follows and (2) that a condition subsequent can only operate to return pos- a life estate. Once it becomes possessory, however, B’s interest session to the grantor, not to a third party. will entitle B to possess the property forever, so the duration of B’s interest is “fee simple absolute.” As this example shows, an interest’s nature describes how it begins; an interest’s duration To A, but if A divorces then O may retake the property. (6) describes how it ends (if at all). Finally, an interest can be subjected to a condition precedent: In the metaphysics of future interests, A’s death is regarded as even if the interest appears to be next in line, it cannot become 0 causing A life estate to expire naturally. It is also possible to add possessory unless and until the condition is satsied. Conveyance a special limitation (which we will simply call a limitation) to an 7 gives a simple example. Here, A’s life estate is followed by B’s interest, as in Conveyance 3. (From here on, we omit the formulaic remainder in life estate and C’s remainder in fee simple. But B’s “O conveys” when it is clear from context. ) remainder has a condition precedent aached. If B is underage at A’s death, B does not take possession immediately. Instead, in most or all states today, O temporarily recovers possession (via an To A for life so long as A lives on the property, then to B (3) implied reversion) until B turns 21 and the condition precedent is satsied. If B dies before then, B’s interest expires before it be- Here, the limitation is created by the phrase ”so long as A comes possessory, and C’s remainder becomes posessory instead. lives on the property,” and it reduces the duration of A’s interest. Now A holds not a life estate but a life estate determinable. e interest will expire at A’s death or when A stops living on the To A for life, then to B for life if B has turned 21, then to C. property, whichever comes rst. Terminologically, it is helpful to (7) break up durations into two halves. e rst part, which some is is a brief survey of the essential concepts. We will say more writers call the quantum and so do we, is “life estate.” ere are about the details in later sections as we walk through (and justify only a small handful of permissible quanta in property law: fee our choices of) semantic rules. simple, life estate, term of years, and a few more. e second part is the limitation, “so long as A lives on the property.” e full 3. Formalizing Conveyances and Interests duration, then, consists of the interest’s quantum together with the special limitation, if any. Nomenclature aside, “To A for life, then to B” and “To A unless An interest can expire naturally, but it can also be cut short A is disbarred, then to B” have a similar structure: an initial in- by a later interest. Conveyance 4 shows an example of interests terest that expires if an event occurs, followed by a second in- potentially divested by a later interest. terest that becomes possessory if it does. e rest of this section denes a model based on this intuition. Our goal is to develop a model that is exible enough to capture common classes of inter- To A for life, then to B, but if C marries to C (4) ests, and that supports computational analysis.