Harvard Law Review Harvard Law Review Harvard Law Review

Constitutional Theory

An Equilibrium-Adjustment Theory of the Fourth Amendment

Fourth Amendment law is often considered a theoretical embarrassment. The law consists of dozens of rules for very specific situations that seem to lack a coherent explanation. Constitutional protection varies dramatically based on seemingly arcane distinctions.

This Article introduces a new theory that explains and justifies both the structure and content of Fourth Amendment rules: the theory of equilibrium-adjustment. The theory of equilibrium-adjustment posits that the Supreme Court adjusts the scope of Fourth Amendment protection in response to new facts in order to restore the status quo level of protection. When changing technology or social practice expands government power, the Supreme Court tightens Fourth Amendment protection; when it threatens government power, the Supreme Court loosens constitutional protection. Existing Fourth Amendment law therefore reflects many decades of equilibrium-adjustment as facts have changed over time. This simple argument explains a wide range of puzzling Fourth Amendment doctrines, including the automobile exception; rules on using sense-enhancing devices; the decline of the mere evidence rule; how the Fourth Amendment applies to the telephone network; undercover investigations; the law of aerial surveillance; rules for subpoenas; and the special Fourth Amendment protection for the home.

The Article then offers a normative defense of equilibrium-adjustment. Equilibrium-adjustment maintains interpretive fidelity while permitting Fourth Amendment law to respond to changing facts. Its wide appeal and focus on deviations from the status quo facilitates coherent decisionmaking amidst empirical uncertainty and yet also gives Fourth Amendment law significant stability. The Article concludes by arguing that judicial delay is an important precondition to successful equilibrium-adjustment.