Also known as: fidem mentitus · fides mentita · breach of faith · perjury
Written by attorneys · grounded in primary & secondary sources — see below
An act by which a feudal tenant violates the oath of fealty sworn to a lord. The phrase captures the breach of sworn loyalty that historically carried legal consequences in feudal systems.
Tenant Thomas swore an oath of fealty to Lord Lambert. Thomas later sold part of the fief to a third party without consent. The lord brought a writ of forfeiture, treating the sale as fidem mentiri that terminated Thomas's tenure.
Vassal Victor secretly aided a neighboring baron who challenged Lord Lambert's title. When the baron invaded, Victor supplied men and arms. The court held Victor's conduct constituted fidem mentiri and declared his lands escheated.
Tenant Terrence performed homage to Lord Lambert while already bound to another lord. The prior oath rendered the new homage void. Lambert sued for fidem mentiri and recovered the fief by judgment of the manorial court.
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Tenant Timothy refused to answer the lord's call to arms during a border skirmish. The lord convened his court and found Timothy guilty of fidem mentiri. Timothy forfeited his holding and was declared an outlaw.
Tenant Theodore granted a sub-tenancy to a stranger without obtaining Lord Lambert's consent. The lord claimed the grant itself was fidem mentiri. The manorial rolls recorded the forfeiture of Theodore's estate.
Tenant Tabitha hid that she owed knight service to the king rather than to Lord Lambert. When the king demanded service, Lambert discovered the concealment. The court declared the concealment fidem mentiri and seized the tenancy.
The phrase originally described a feudal tenant's breach of sworn loyalty to a lord. The concept of broken fealty later influenced the development of perjury as a distinct legal wrong.
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No. Fidem mentiri concerns breach of a feudal oath of loyalty, not testimonial inconsistency in later judicial proceedings.
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No. Bias impeachment addresses credibility in court. Fidem mentiri addresses violation of a feudal tenant's oath to a lord.
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The signature requirement is unrelated to fidem mentiri, which concerns feudal breach of fealty rather than modern authentication rules.
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