Whether duress sufficient to avoid a conveyance is measured chiefly by an objective standard of ordinary firmness or by whether wrongful pressure in fact overcame this party's free will.
Holding
Duress is assessed primarily by a subjective inquiry: wrongful threats or pressure may render a conveyance voidable when they actually overcome the particular person's will and induce an act he otherwise would not have taken.
Reasoning
Consent is indispensable to a valid contract or conveyance. Actual physical violence is unnecessary; threats of death, grave bodily harm, imprisonment, or comparable moral and psychological compulsion can negate real consent when they deprive a person of free agency.
The older common-law formulations asked whether threats would put a brave person, or a person of ordinary firmness, in fear. The modern and better rule asks whether the pressure actually controlled the will of the person subjected to it. The person's age, sex, capacity, relationship with the alleged coercer, and all surrounding circumstances bear on that inquiry.
The pressure must be wrongful, although it need not be technically unlawful. Even conduct or legal means that are ordinarily lawful may constitute duress when used so oppressively that they constrain a person to do what his free will would reject. Duress is akin to fraud because it concerns the unreality of apparent consent, though it does not require an intent to deceive by the person applying the pressure.