Necessary Legal Background
THE U.S. LEGAL SYSTEM SHARES MANY FEATURES WITH THE SCIENCE OF geology. According to geologists, new rocks are laid down over the old in a continual process of building. Newer rocks may command more immediate attention, but the old rocks are still there, deeper but providing a foundation for the new. The process of accretion of new material over old resembles the growth of the law. New decisions are continually added to the body of the old, but the old law still remains as foundation. In legal terminology, this is the principle of stare decisis. New court decisions and laws continually build upon and add to the older body of law, but the old decisions remain and become the substratum on which the newer decisions stand. More recent decisions must be based on the precedents established by prior court decisions.
Rock formations, like legal decisions, can extend over large expanses of territory, or they can be local and unique. This situation is analogous to the legal principle of controlling authority. Subsequent court decisions cannot contradict prior decisions that are controlling in its jurisdictional area, except on the rare occasions where a court declares that its own former ruling is no longer good law. Said another way, not every court decision has the power to influence subsequent decisions in every locality. Some decisions apply only locally; others are more geographically widespread in their applicability. For example, a Pennsylvania Commonwealth Court ruling that a certain school district in Chester County,