Non Est Factum Legal Definition: Latin: not his deed. Related Terms: Mistake , Consensus Ad Idem , Animus Contrahendi A special defense in contract law to allow a person to avoid having to respect a contract that she or he signed because of certain reasons such as a mistake as to the kind of contract. For example, a person who signs away the deed to a house, thinking that the document signed was only a guarantee for another person's debt, might be able to plead non est factum in a court and on that basis get the court to void the contract. Justice Cartwright of Canada's Supreme Court used these delightful words to describe non est factum in Marvco Colour Research Ltd. v. Harris: "(W)here a document was executed as a result of a misrepresentation as to its nature and character and not merely its contents the defendant was entitled to raise the plea of non est factum on the basis that his mind at the time of the execution of the document did not follow his hand." The "did not follow his hand" theme was continued by Justice LaForme in Beer v Beer: "Non est factum is a defence whose application is restricted to those circumstances where the person relying on it must show; (1) they were not careless, and (2) the document sdigned was different from the one theythought they were signing." Note these words of Justice Cusinato of the Ontario Superior Court of Justice in Piccolo v. Dibenedetto: "The use and application of the principle of non est factum generally is applicable as a shield and not a sword... "…generally speaking, a person who executes a document without taking the trouble to read it is liable on it and cannot plead that he mistook its contents, at all events, as against a person who acting in good faith in the ordinary course of business has changed his position in reliance on such document." This topic of contract law is discussed at length in Duhaime's Contract Law, Chapter 5. REFERENCES: Beer v Beer, 13 RPR (3d) 33 (1997) Marvco Colour Research Ltd. v. Harris,  2 SCR 774 Piccolo v. Dibenedetto, 62 OR (3d) 66 (2002) Categories & Topics: Dictionary of Latin Law Terms Duhaime's Contract Law Dictionary Unless otherwise noted, this page was written by Lloyd Duhaime of Duhaime.org Always looking up definitions? Save time with our search provider (modern browsers only) If you find an error or omission in Duhaime's Law Dictionary, or if you have suggestion for a legal term, we'd love to hear from you!