Where a person is prevented from acting (or not acting) according to their free will, by threats or force of another, it is said to be under duress.
Contracts signed under duress are voidable and, in may places, you cannot be convicted of a crime if you can prove that you were forced or threatened into committing the crime (although this defence may not be available for serious crimes).
In AV v iParadigms, Justice Claude Hilton of the United States District Court (Virginia), wrote:
"In Virginia, duress is defined as the overbearing of a person's free will by an unlawful or wrongful act or by threat such that the party's consent to a contractual agreement is involuntary."
Or, consider these words of Chief Justice Robert Gross of the District Court of Appeal of Florida in Francaville:
"[D]uress is a condition of mind produced by an improper external pressure or influence that practically destroys the free agency of a party and causes him to do an act or make a contract not of his own volition.
"Two factors must be proven to establish duress: (a) that the act sought to be set aside was effected involuntarily and thus not as an exercise of free choice or will and (b) that this condition of mind was caused by some improper and coercive conduct of the opposite side.
"Duress involves a dual concept of external pressure and internal surrender or loss of volition in response to outside compulsion."
Duress can be in regards to threatened physical harm or economic duress.
In Brown v United States, Justice Holmes wrote that:
"Detached reflection cannot be demanded in the presence of an uplifted knife".
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