Objection 1. It would seem that a betrothal cannot be dissolved if one of the parties enter religion. For if I have promised a thing to someone I cannot lawfully pledge it to someone else. Now he who betroths himself promises his body to the woman. Therefore he cannot make a further offering of himself to God in religion.
Objection 2. Again, seemingly it should not be dissolved when one of the parties leaves for a distant country, because in doubtful matters one should always choose the safer course. Now the safer course would be to wait for him. Therefore she is bound to wait for him.
Objection 3. Again, neither seemingly is it dissolved by sickness contracted after betrothal, for no man should be punished for being under a penalty. Now the man who contracts an infirmity would be punished if he were to lose his right to the woman betrothed to him. Therefore a betrothal should not be dissolved on account of a bodily infirmity.
Objection 4. Again, neither seemingly should a betrothal be dissolved on account of a supervening affinity, for instance if the spouse were to commit fornication with a kinswoman of his betrothed; for in that case the affianced bride would be penalized for the sin of her affianced spouse, which is unreasonable.
Objection 5. Again, seemingly they cannot set one another free; for it would be a proof of greatest fickleness if they contracted together and then set one another free; and such conduct ought not to be tolerated by the Church. Therefore, etc.
Objection 6. Again, neither seemingly ought a betrothal to be dissolved on account of the fornication of one of the parties. For a betrothal does not yet give the one power over the body of the other; wherefore it would seem that they nowise sin against one another if meanwhile they commit fornication. Consequently a betrothal should not be dissolved on that account.
Objection 7. Again, neither seemingly on account of his contracting with another woman by words expressive of the present. For a subsequent sale does not void a previous sale. Therefore neither should a second contract void a previous one.
Objection 8. Again, neither seemingly should it be dissolved on account of deficient age; since what is not cannot be dissolved. Now a betrothal is null before the requisite age. Therefore it cannot be dissolved.
I answer that, In all the cases mentioned above the betrothal that has been contracted is dissolved, but in different ways. For in two of them--namely when a party enters religion, and when either of the affianced spouses contracts with another party by words expressive of the present--the betrothal is dissolved by law, whereas in the other cases it has to be dissolved according to the judgment of the Church.
Reply to Objection 1. The like promise is dissolved by spiritual death, for that promise is purely spiritual, as we shall state further on (61, 2).
Reply to Objection 2. This doubt is solved by either party not putting in an appearance at the time fixed for completing the marriage. Wherefore if it was no fault of that party that the marriage was not completed, he or she can lawfully marry without any sin. But if he or she was responsible for the non-completion of the marriage, this responsibility involves the obligation of doing penance for the broken promise--or oath if the promise was confirmed by oath--and he or she can contract with another if they wish it, subject to the judgment of the Church.
Reply to Objection 3. If either of the betrothed parties incur an infirmity which notably weakens the subject (as epilepsy or paralysis), or causes a deformity (as loss of the nose or eyes, and the like), or is contrary to the good of the offspring (as leprosy, which is wont to be transmitted to the children), the betrothal can be dissolved, lest the betrothed be displeasing to one another, and the marriage thus contracted have an evil result. Nor is one punished for being under a penalty, although one incurs a loss from one's penalty, and this is not unreasonable.
Reply to Objection 4. If the affianced bridegroom has carnal knowledge of a kinswoman of his spouse, or "vice versa," the betrothal must be dissolved; and for proof it is sufficient that the fact be the common talk, in order to avoid scandal; for causes whose effects mature in the future are voided of their effects, not only by what actually is, but also by what happens subsequently. Hence just as affinity, had it existed at the time of the betrothal, would have prevented that contract, so, if it supervene before marriage, which is an effect of the betrothal, the previous contract is voided of its effect. Nor does the other party suffer in consequence, indeed he or she gains, being set free from one who has become hateful to God by committing fornication.
Reply to Objection 5. Some do not admit this case. Yet they have against them the Decretal (cap. Praeterea, De spons. et matr.) which says expressly: "Just as those who enter into a contract of fellowship by pledging their faith to one another and afterwards give it back, so it may be patiently tolerated that those who are betrothed to one another should set one another free." Yet to this they say that the Church allows this lest worse happen rather than because it is according to strict law. But this does not seem to agree with the example quoted by the Decretal.
Accordingly we must reply that it is not always a proof of fickleness to rescind an agreement, since "our counsels are uncertain" (Wisdom 9:14).
Reply to Objection 6. Although when they become betrothed they have not yet given one another power over one another's body, yet if this [Referring to the contention of the Objection] were to happen it would make them suspicious of one another's fidelity; and so one can ensure himself against the other by breaking off the engagement.
Reply to Objection 7. This argument would hold if each contract were of the same kind; whereas the second contract of marriage has greater force than the first, and consequently dissolves it.
Reply to Objection 8. Although it was not a true betrothal, there was a betrothal of a kind; and consequently, lest approval should seem to be given when they come to the lawful age, they should seek a dissolution of the betrothal by the judgment of the Church, for the sake of a good example.
Source: Summa Theologica (New Advent)