Vows are perpetual if the obligation is undertaken for life; otherwise they are temporary.
A solemn vow is one which is invested by the Church with special force and stability, together with certain legal effects; others are simple. The vows taken by religious in regular orders specially approved by the Pope, and by those who receive sacred orders, are solemn.
2. Substantial mistake about the matter of a vow or about the circumstances which are regarded as entering into the substance of the matter invalidates a vow. For substantial mistake hinders consent of the will; consent was given to something which was not there, and so there was no contract. A vow, then, dedicating to God a chalice which is thought to be silver, while in reality it is gold, would be invalid, just as a sale of it would be under the same mistake. Merely accidental mistake about things of little moment which were not really the motive for taking a vow does not invalidate it. However, according to St Alphonsus, [1] it is a probable opinion that a mistake about something connected with a vow, which if it had been known before would have prevented its being taken, is sufficient to invalidate it. This doctrine may be applied to private vows, but it cannot be extended to the vows of religion, which place the religious in a permanent state of life. In order to invalidate these, mistake must be substantial. For just as the perpetuity of the state of marriage, 4 the good of the parties concerned, and the public good, require that only substantial mistake should invalidate marriage, so for the same reasons only substantial mistake invalidates the vows of religion, by which the religious enters into mystical espousals with Christ.
Fear arising from natural causes, provided that it does not take away the use of reason, does not invalidate a vow. If, however, grave fear be unjustly caused with a view to compelling another to take a vow, the. vow is null and void (Can. 1307). The same is probably true even if the fear be slight. For God cannot be supposed to accept a promise which has not been freely given, but on the contrary extorted by unjust violence.
3. A vow, as we have seen, imposes a special obligation on him who has taken it to perform what he has promised: " If thou hast vowed anything to God, defer not to pay it; for an unfaithful and foolish promise displeaseth him: but whatsoever thou hast vowed, pay it." [2] If a special time was fixed for the
