I answer that, The manner in which a thing is solemnized depends on its nature (conditio): thus when a man takes up arms he solemnizes the fact in one way, namely, with a certain display of horses and arms and a concourse of soldiers, while a marriage is solemnized in another way, namely, the array of the bridegroom and bride and the gathering of their kindred. Now a vow is a promise made to God: wherefore, the solemnization of a vow consists in something spiritual pertaining to God; i.e. in some spiritual blessing or consecration which, in accordance with the institution of the apostles, is given when a man makes profession of observing a certain rule, in the second degree after the reception of holy orders, as Dionysius states (Eccl. Hier. vi). The reason of this is that solemnization is not wont to be employed, save when a man gives himself up entirely to some particular thing. For the nuptial solemnization takes place only when the marriage is celebrated, and when the bride and bridegroom mutually deliver the power over their bodies to one another. In like manner a vow is solemnized when a man devotes himself to the divine ministry by receiving holy orders, or embraces the state of perfection by renouncing the world and his own will by the profession of a certain rule.
Reply Obj. 1: This kind of solemnization regards not only men but also God in so far as it is accompanied by a spiritual consecration or blessing, of which God is the author, though man is the minister, according to Num. 6:27, "They shall invoke My name upon the children of Israel, and I will bless them." Hence a solemn vow is more binding with God than a simple vow, and he who breaks a solemn vow sins more grievously. When it is said that a simple vow is no less binding than a solemn vow, this refers to the fact that the transgressor of either commits a mortal sin.
Reply Obj. 2: It is not customary to solemnize particular acts, but the embracing of a new state, as we have said above. Hence when a man vows particular deeds, such as a pilgrimage, or some special fast, such a vow is not competent to be solemnized, but only such as the vow whereby a man entirely devotes himself to the divine ministry or service: and yet many particular works are included under this vow as under a universal.
Reply Obj. 3: Through being pronounced in public vows may have a certain human solemnity, but not a spiritual and divine solemnity, as the aforesaid vows have, even when they are pronounced before a few persons. Hence the publicity of a vow differs from its solemnization. _______________________
EIGHTH ARTICLE [II-II, Q. 88, Art. 8]
Whether Those Who Are Subject to Another's Power Are Hindered from
Taking Vows?
Objection 1: It would seem that those who are subject to another's power are not hindered from taking vows. The lesser bond is surpassed by the greater. Now the obligation of one man subject to another is a lesser bond than a vow whereby one is under an obligation to God. Therefore those who are subject to another's power are not hindered from taking vows.
Obj. 2: Further, children are under their parents' power. Yet children may make religious profession even without the consent of their parents. Therefore one is not hindered from taking vows, through being subject to another's power.
Obj. 3: Further, to do is more than to promise. But religious who are under the power of their superiors can do certain things such as to say some psalms, or abstain from certain things. Much more therefore seemingly can they promise such things to God by means of vows.
Obj. 4: Further, whoever does what he cannot do lawfully sins. But subjects do not sin by taking vows, since nowhere do we find this forbidden. Therefore it would seem that they can lawfully take vows.