2196. Freedom of Will Necessary for Valid Vow.—In the will of the person who takes a vow there must be freedom of choice, and the absence of such impediments as take away self-determination or consent.
(a) Thus, the natural law itself invalidates a vow made under force or under such fear as takes away the power of giving due deliberation to the vow.
(b) The natural law, according to many, invalidates a vow made under fear that is grave (though not disturbing to the reason), and that is produced unjustly and with a view to coerce one into making the vow. The reason for this opinion is that God cannot accept a promise to Himself caused by injustice, nor can one be held to a promise made under unjust pressure.
(c) The positive law (see Canon 1307, Sec.3) invalidates a vow given under grave and unjust fear. Many canonists interpret this law as meaning that even when the unjust fear is not employed as a means to force one into taking the vow, but does in reality cause one to take the vow, the promise is null in both forums in virtue of Canon Law.
2197. Cases in Which Fear Does Not Invalidate a Vow.—(a) All admit that fear does not invalidate when it proceeds from a natural cause (e.g., vows made during a storm at sea) or an internal cause (e.g., vows made under the influence of fear that one will fall into sin without the protection of the vow); for in these cases one chooses a lesser burden to avoid a greater one, and the thing chosen is involuntary, not simply, but only in a certain respect (see 44).
(b) It is commonly admitted that fear does not invalidate when it proceeds from an external and just cause (e.g., if a guilty person were threatened with the penalties of law unless he vowed not to repeat the offense), since the cause of the vow is then internal rather than external, namely, the guilt of the person who takes the vow and his wish to evade punishment.
2198. Vows of Doubtful Validity.—In the following cases it is disputed whether fear invalidates a vow.
(a) It is disputed whether fear unjustly caused invalidates in the forum of conscience when it is light (e.g., Titia constantly importuned by her parents to enter religion makes a vow to follow their wishes). Some answer in the negative, because a fear that is slight both in itself and in its influence on the vower cannot be considered as the real cause of the vow. Others answer in the affirmative, because light reasons do move persons to take grave steps, and it is not reasonable to think that God will accept a vow brought on by unjust, though light, fear.
(b) It is also disputed whether grave fear unjustly caused invalidates, when the person who causes the fear intends to force the vower, not to the vow, but to something else (e.g., Balbus threatens to kill Caius unless the latter pays a large sum of money, and Caius vows to give the money to religion if he escapes the danger). Some hold for the affirmative and refer to Canon 1307, mentioned above. Others hold for the negative because the vow is taken, not to accommodate the aggressor, but to honor God and benefit self. This is the interpretation given the pre-Code legislation. Still others distinguish, affirming invalidity for the case in which fear is the cause of the vow and denying invalidity for the case when fear is only the occasion of the vow.
2199. The Intention Necessary for a Valid Vow.—As was said in the explanation of the definition, a vow must include a will to bind oneself, that is, the intention to make a vow.