1.   Someone must always own (be seized of) each freehold estate in land.

2.   Courts should interpret property interests so as to give effect to the creator’s intent where that intent is not inconsistent with the law (public policy), a consequence of the statute de donis conditionalibus in 1285 (Statute of Westminster II, 13 Edw. I).

3.   The law should promote the free alienability (transferability) of property interests, a consequence of the statute Qui Emptores in 1290 (18 Edw. I).

4.   The law favors "productive use" of property.

Each of these Central Operating Principles (COPs) developed to support the Crown's exercise of its absolute ownership of England and its need to exercise political control over all of that country. Initially, they developed from intended and unintended consequences of the unique feudal system of land ownership or tenure that William the Conqueror and his successors imposed. However, as the strength of that system eroded over the centuries, these principles proved useful to new property owners and new societal needs. They have long outlived the system that first gave them currency because they continue to reflect the interests and desires of property owners, even as the nature of society and of property changes.

COP 2, COP 3, and COP 4 sometimes conflict with one another. A desire to give effect to the intent of a transferor long dead can frustrate the desire of the current owner to use or transfer property interests free of restrictions imposed by that earlier owner. The ways in which courts deal with the overlap between these COPs is responsible for much of the flexibility of modern American property law. You should look for them in each of the Chapters to come.