Legal Definitions - de son tort demesne

De son tort demesne is a legal phrase originating from Law French, which translates to "of one's own wrong." This principle is invoked when a party's own prior wrongful conduct, unauthorized action, or breach of duty prevents them from relying on a particular defense or justification for their subsequent actions. Essentially, it means that a person cannot excuse their behavior or benefit from a situation that they themselves created through their initial misconduct or lack of authority.

Here are some examples illustrating this concept:

• Example 1 (Trespass and Injury): Imagine a person, Sarah, who unlawfully enters a private construction site, ignoring prominent "No Trespassing" signs. While on the site, Sarah trips over a piece of equipment that was negligently left out by the construction company. If Sarah attempts to sue the construction company for negligence, the company might argue de son tort demesne. This means Sarah cannot claim the company was solely at fault for her injury because her own initial wrongful act (trespassing) put her in a position to be injured in the first place, thereby undermining her claim for damages.

• Example 2 (Contract Breach): Consider a scenario where a marketing agency, "Creative Campaigns," is contracted to launch a new product campaign by a specific date. Creative Campaigns intentionally delays the project for several weeks without a valid reason, missing the agreed-upon deadline. When the client, "Tech Innovations," refuses to pay the final installment due to the delay, Creative Campaigns attempts to argue that Tech Innovations failed to provide certain necessary images on time, which contributed to the delay. Tech Innovations could invoke de son tort demesne, asserting that Creative Campaigns' own initial breach of contract (the intentional, significant delay) prevents them from using Tech Innovations' alleged minor delay in providing images as a valid excuse for their own substantial failure.

• Example 3 (Unauthorized Action by an Agent): Suppose a real estate agent, Mark, is hired to manage a rental property. The management agreement explicitly states that any major repairs exceeding a certain cost require prior written approval from the property owner, Lisa. Mark proceeds to commission an expensive roof replacement without obtaining Lisa's consent. When Lisa refuses to reimburse Mark for the unauthorized expense, Mark tries to justify his action by claiming the roof was in urgent need of repair to prevent further damage. Lisa could argue de son tort demesne, meaning Mark cannot use the supposed "necessity" of the repair as a defense because his initial act of commissioning an expensive repair without authorization was his own wrong, violating the terms of their agreement.