Legal Definitions - ex paritate rationis

Ex paritate rationis is a Latin legal phrase that translates to "by a parity of reasoning." This principle allows legal professionals and courts to extend an established legal rule, precedent, or principle from one specific situation to a different, but fundamentally similar, situation. It is applied when the underlying reasons, logic, or policy that justify the existing rule are equally applicable to the new scenario, even if the new scenario is not explicitly covered by the original rule or law. Essentially, if the rationale behind a rule applies equally to a new case, then the rule itself should also apply.

• Example 1: Contract Law

  Imagine a jurisdiction where there is a long-standing legal precedent stating that contracts for the sale of physical goods implicitly include a warranty that the goods are fit for their ordinary purpose, even if not explicitly written into the contract. This protects buyers from receiving defective products. Now, a new type of contract emerges for the licensing of digital software, which is not a "physical good" in the traditional sense. A court might decide that, ex paritate rationis, the principle of an implied warranty of fitness for ordinary purpose should also apply to software licensing agreements. The reasoning is that consumers expect software to function as intended, just as they expect physical goods to work. The underlying rationale for protecting consumers from defective products applies equally to defective software, even though the original precedent only mentioned "goods."

• Example 2: Regulatory Law

  Consider a city ordinance that prohibits loud noise disturbances from residential properties between 10 PM and 7 AM, with the stated purpose of protecting residents' peace and quiet. Over time, a new phenomenon arises: short-term rental properties (like those booked through online platforms) operating within residential zones. While these might technically be considered commercial activities, they are situated within residential buildings and neighborhoods. A local government or court could rule that, ex paritate rationis, the noise ordinance designed for traditional residential properties should also apply to short-term rentals. The fundamental reason for the ordinance – protecting the peace and quiet of residential neighborhoods – applies equally to noise emanating from a short-term rental as it does from a permanent residence. The nature of the disturbance and its impact on neighbors remains the same, regardless of the property's specific use classification.