Fourth Amendment doctrine is attentive to a wide range of interests, including security, informational privacy, and dignity. How should courts reconcile these competing concerns when deciding which searches and seizures are “unreasonable”? Current doctrine typically answers this question by pointing to interest aggregation: the various interests at stake are added up, placed on figurative scales, and compared, with the goal of promoting overall social welfare. But interest aggregation is disconnected from many settled doctrinal rules and leads to results that are unfair for individuals. The main alternative is originalism; but historical sources themselves suggest that the Fourth Amendment calls for new moral reasoning.

This Article argues that the Fourth Amendment’s prohibition on “unreasonable searches and seizures” is best understood, at least in large part, as a requirement that police investigation be fair in the sense of being authorized by principles that no rights holder could reasonably reject. This approach is inspired by “contractualist” moral philosophy and has several advantages. It tracks widely held moral intuitions, comports with the Fourth Amendment’s historical meaning, and resonates with underappreciated currents in extant case law. In attending to the perspectives of individuals, contractualism generates rights that are not subject to interest aggregation. At the same time, contractualism suggests a principled way to address new Fourth Amendment questions, consistent with courts’ institutional role.

A contractualist approach to Fourth Amendment fairness suggests many ways to refine or reform current doctrine. In terms of refinements, the contractualist approach gives moral content to the notion of “individualized suspicion” by showing when searches and seizures can be justified by a principle of individual responsibility. Contractualism also draws attention to other justifying principles, such as a protection principle, and so explains how and when suspicionless searches and seizures are reasonable. Finally, the contractualist approach identifies areas where current Fourth Amendment doctrine is decidedly unfair and ripe for reform, such as when courts limit rights to avoid diffuse litigation costs, overemphasize “reasonable expectations of privacy,” and ignore the unreasonableness of racial discrimination.