Legal Definitions - expressio unius est exclusio alterius

The Latin phrase expressio unius est exclusio alterius translates to "the expression of one thing is the exclusion of another."

This is a principle of legal interpretation which suggests that when a law, contract, or other legal document explicitly lists certain items, conditions, or actions, it implies that any items, conditions, or actions not mentioned are deliberately excluded. In essence, by specifically including some things, the document implicitly excludes all others that are not listed.

Here are some examples to illustrate this principle:

• Example 1: Residential Lease Agreement

  Imagine a clause in a residential lease agreement that states: "Tenants are permitted to keep up to two indoor cats, provided they are spayed or neutered and have current vaccination records."

  How it illustrates the term: By explicitly mentioning and setting conditions for "indoor cats," the lease agreement, through expressio unius est exclusio alterius, implies that other types of pets—such as dogs, birds, reptiles, or outdoor cats—are not allowed on the property. The landlord chose to express permission for a specific type of pet, thereby implicitly excluding all others.

• Example 2: City Park Ordinance

  A local city ordinance regarding public parks declares: "The following activities are permitted in Central Park between sunrise and sunset: picnicking, walking, jogging, and playing non-amplified music."

  How it illustrates the term: By specifically listing picnicking, walking, jogging, and non-amplified music as permitted activities, the ordinance, through expressio unius est exclusio alterius, implies that any activities not on this list—such as camping, skateboarding, operating drones, or playing amplified music—are prohibited. The city council chose to enumerate specific allowances, thereby excluding unlisted activities.

• Example 3: Company Expense Policy

  A company's employee expense reimbursement policy states: "Employees will be reimbursed for approved business travel expenses including airfare, hotel accommodation, and ground transportation via taxi or ride-sharing services."

  How it illustrates the term: This policy explicitly lists airfare, hotel, and specific ground transportation as reimbursable expenses. According to expressio unius est exclusio alterius, this specific enumeration implies that other potential travel-related costs, such as personal car mileage, meals, or entertainment expenses, are *not* covered for reimbursement unless explicitly stated elsewhere in the policy. The company's specific inclusion of certain items suggests the deliberate exclusion of others.