If a Catholic is marrying a Protestant, I read that both parties must be instructed about the purposed and essential properties of marriage, which neither party is to exclude.
In other words, does this mean the non-Catholic party has to promise not use birth control?
It is more a matter of proper consent, it could indicate the presence of improper consent, although it does not indicate it by itself, yer per Robert J. Flummerfelt, J.C.L.:
If the pill is used, the ‘human manner’ portion is fulfilled and the marriage is indeed consummated, BUT this clearly [if done regularly]would INVALIDATE the marriage since there was no openness to children. Plus, on a moral level, obviously this is objectively wrong not only for inhibiting conception, BUT ALSO in some circumstances since the pill works as an abortifacient.
The marriage may not be consummated through conjugal relations using a condom.
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Two key concepts from canon law (CIC) are:
Can. 1056 The essential properties of marriage are unity and indissolubility, which in Christian marriage obtain a special firmness by reason of the sacrament.
Can. 1096 §1. For matrimonial consent to exist, the contracting parties must be at least not ignorant that marriage is a permanent partnership between a man and a woman ordered to the procreation of offspring by means of some sexual cooperation.
And also per canon law, such as impediments, must be considered:
Can. 1059 Even if only one party is Catholic, the marriage of Catholics is governed not only by divine law but also by canon law, without prejudice to the competence of civil authority concerning the merely civil effects of the same marriage.