“A system of private ownership must provide for something more sophisticated than absolute ownership of the property by one person. A property owner needs to be able to do more than own it during his lifetime and pass it on to someone else on his death.”1 Those who own things with a long life quite naturally feel the urge to deal in segments of time. Most of the owner's ambitions in respect of time can be met by the law of contract. But contract does not offer a complete solution, since contracts create only personal rights. Certain of the owner's legitimate wishes can be achieved only if the law allows them to be given effect in rem—that is, as proprietary rights. Legal systems have responded differently to the need for proprietary rights limited in time. Roman law created usufruct and other iura in re aliena; English law created different legal estates. Every system has faced similar problems. One issue has been the extent to which the holder of a limited interest should be restricted in his or her use and enjoyment in order to protect the holders of other interests in the same thing. A common core of principles regulates the relationship between those who hold temporary interests and the reversioners. For instance, every system forbids holder of the possessory interest to damage the thing arbitrarily. But other rules are more controversial. This study focuses upon the rules which do not forbid, but compel, certain courses of action.
