Objection 1: It would seem that vows are not all binding. For man needs things that are done by another, more than God does, since He has no need for our goods (Ps. 15:2). Now according to the prescription of human laws [*Dig. L. xii, de pollicitat., i] a simple promise made to a man is not binding; and this seems to be prescribed on account of the changeableness of the human will. Much less binding therefore is a simple promise made to God, which we call a vow.
Obj. 2: Further, no one is bound to do what is impossible. Now sometimes that which a man has vowed becomes impossible to him, either because it depends on another's decision, as when, for instance, a man vows to enter a monastery, the monks of which refuse to receive him: or on account of some defect arising, for instance when a woman vows virginity, and afterwards is deflowered; or when a man vows to give a sum of money, and afterwards loses it. Therefore a vow is not always binding.
Obj. 3: Further, if a man is bound to pay something, he must do so at once. But a man is not bound to pay his vow at once, especially if it be taken under a condition to be fulfilled in the future. Therefore a vow is not always binding.
On the contrary, It is written (Eccles. 5:3, 4): "Whatsoever thou hast vowed, pay it; and it is much better not to vow, than after a vow not to perform the things promised."
I answer that, For one to be accounted faithful one must keep one's promises. Wherefore, according to Augustine [*Ep. xxxii, 2: De Mendac. xx] faith takes its name "from a man's deed agreeing with his word" [*Fides . . . fiunt dicta. Cicero gives the same etymology (De Offic. i, 7)]. Now man ought to be faithful to God above all, both on account of God's sovereignty, and on account of the favors he has received from God. Hence man is obliged before all to fulfill the vows he has made to God, since this is part of the fidelity he owes to God. On the other hand, the breaking of a vow is a kind of infidelity. Wherefore Solomon gives the reason why vows should be paid to God, because "an unfaithful . . . promise displeaseth Him" [*Eccles. 5:3].
Reply Obj. 1: Honesty demands that a man should keep any promise he makes to another man, and this obligation is based on the natural law. But for a man to be under a civil obligation through a promise he has made, other conditions are requisite. And although God needs not our goods, we are under a very great obligation to Him: so that a vow made to Him is most binding.
Reply Obj. 2: If that which a man has vowed becomes impossible to him through any cause whatsoever, he must do what he can, so that he have at least a will ready to do what he can. Hence if a man has vowed to enter a monastery, he must endeavor to the best of his power to be received there. And if his intention was chiefly to bind himself to enter the religious life, so that, in consequence, he chose this particular form of religious life, or this place, as being most agreeable to him, he is bound, should he be unable to be received there, to enter the religious life elsewhere. But if his principal intention is to bind himself to this particular kind of religious life, or to this particular place, because the one or the other pleases him in some special way, he is not bound to enter another religious house, if they are unwilling to receive him into this particular one. On the other hand, if he be rendered incapable of fulfilling his vow through his own fault, he is bound over and above to do penance for his past fault: thus if a woman has vowed virginity and is afterwards violated, she is bound not only to observe what is in her power, namely, perpetual continency, but also to repent of what she has lost by sinning.
Reply Obj. 3: The obligation of a vow is caused by our own will and intention, wherefore it is written (Deut. 23:23): "That which is once gone out of thy lips, thou shalt observe, and shalt do as thou hast promised to the Lord thy God, and hast spoken with thy own will and with thy own mouth." Wherefore if in taking a vow, it is one's intention and will to bind oneself to fulfil it at once, one is bound to fulfil it immediately. But if one intend to fulfil it at a certain time, or under a certain condition, one is not bound to immediate fulfilment. And yet one ought not to delay longer than one intended to bind oneself, for it is written (Deut. 23:21): "When thou hast made a vow to the Lord thy God thou shalt not delay to pay it: because the Lord thy God will require it; and if thou delay, it shall be imputed to thee for a sin."