Legal Definitions - rei interventus

rei interventus

Rei interventus describes a legal principle where an agreement, even if not fully formalized in writing, becomes binding because one party has taken significant actions or performed part of their obligations with the explicit knowledge and consent of the other party. These actions demonstrate a reliance on the agreement, making it unfair for the other party to later deny its existence or back out without being considered in breach. Essentially, it prevents a party from repudiating an agreement after allowing the other party to act upon it.

Here are some examples to illustrate this concept:

• Scenario: A verbal agreement for custom software development.

  A small business owner verbally agrees with a software developer to create a custom application for their operations. While a formal contract is still being drafted, the business owner provides the developer with detailed specifications, access to their existing systems, and gives explicit permission to begin preliminary coding and database setup. The developer spends two weeks on these initial tasks. If the business owner then tries to cancel the project, claiming no formal contract was ever signed, the developer could argue rei interventus. The business owner's consent to the developer's partial performance (preliminary coding, setup) makes the agreement binding, and they cannot now repudiate it without being in breach.

• Scenario: A handshake deal for a commercial lease.

  A property owner and a prospective tenant shake hands on a deal to lease a retail space, agreeing on the monthly rent and lease duration. Before the written lease agreement is finalized, the property owner gives the tenant permission to measure the space and bring in contractors to get quotes for renovations specific to their business. The tenant invests time and money in these preparations. If the property owner subsequently tries to lease the space to someone else, the tenant could invoke rei interventus. The property owner's consent to the tenant's preparatory actions (measuring, getting quotes) constitutes partial performance and reliance, making the verbal lease agreement enforceable.

• Scenario: An unwritten agreement for event planning services.

  A client verbally hires an event planner for their upcoming corporate gala, discussing themes, guest lists, and budget. The client then asks the planner to secure a specific venue and caterer immediately, as they are in high demand, and provides the necessary authorization. The planner successfully books both, paying deposits out of their own funds, with the client's full knowledge and approval. If the client later decides to cancel the event planner's services, arguing no written contract was ever signed, the planner could rely on rei interventus. The client's consent to the planner's actions (booking venue and caterer, paying deposits) demonstrates partial performance and reliance, making the agreement binding and preventing the client from backing out without consequence.