Legal Definitions - casus rarior

The term casus rarior, from Latin, refers to an exceptional case or an unusual circumstance that falls outside the typical or expected situations addressed by standard legal rules or precedents. It describes a scenario that is rare, uncommon, or presents unique facts that make it difficult to apply conventional legal principles directly.

• Example 1: Contract Law

  Imagine a contract for the sale of a unique, custom-built yacht. After the contract is signed but before the buyer takes possession, an extremely rare, localized seismic event causes a previously unknown geological fault line directly beneath the shipyard to shift, resulting in structural damage to the yacht that is not covered by standard insurance policies or typical "acts of God" clauses. This would be considered a casus rarior because the specific nature and cause of the damage (a highly localized, unforeseen geological event impacting a specific item) are so unusual that the contract likely doesn't have a clear provision for it, requiring the parties or a court to address an exceptional set of facts.

• Example 2: Property Law

  Consider a dispute between two neighbors over a shared fence line. Decades ago, a rare, highly migratory species of tree, protected by obscure environmental laws, spontaneously grew precisely on the property line, its roots intertwining with the original survey markers and its trunk eventually becoming the de facto boundary. Over time, the tree's growth has subtly shifted the perceived boundary, making it impossible to determine the original line without destroying the protected tree. This situation presents a casus rarior because the unique intersection of environmental protection, natural growth, and property demarcation creates an exceptional challenge not typically encountered in boundary disputes, which usually rely on clear deeds, surveys, or adverse possession rules.

• Example 3: Procedural Law

  In a complex civil litigation, a crucial piece of digital evidence, stored on a secure server, becomes inaccessible not due to a system malfunction or a cyberattack, but because a highly experimental, government-mandated electromagnetic pulse test, conducted in a remote area, inadvertently and unforeseeably corrupted the specific data storage medium through an unknown quantum effect. This would be a casus rarior because the method of data loss is extraordinarily unique and beyond the scope of typical discovery rules concerning spoliation of evidence, accidental deletion, or standard hacking incidents, presenting an exceptional procedural hurdle for the court.