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 One whose vow has been commuted is always at liberty to return if he pleases to the observance of his vow, for the commutation was made in his favour, and he may renounce it.

When a vow has been commuted by competent authority its obligation is extinguished or transferred to the new work, and it does not revive even if the performance of the substituted good work is found to be impossible. On the contrary, when the substitution has been made by private authority, in case the performance of the substituted work is impossible, the original obligation revives.