Suppose that a Catholic man and woman exchange vows in a marriage ceremony, with proper consent, before a Catholic priest. At that point in time, their marriage is ratified, but not yet consummated. When subsequently they engage in natural marital relations open to life, then they have the full Sacrament of holy Matrimony. For only then is their marriage both ratified and consummated.
Canon Law 1061 n. 1: A valid marriage between the baptized is called ratum tantum if it has not been consummated; it is called ratum et consummatum if the spouses have performed between themselves in a human fashion a conjugal act which is suitable in itself for the procreation of offspring, to which marriage is ordered by its nature and by which the spouses become one flesh.”
According to Canon Law, the only sexual act that is able to consummate a marriage, changing the state of their relationship from ratum tantum (ratified only) to ratum et consummatum (ratified and consummated) is natural marital relations open to life. This sexual act must be “suitable in itself for the procreation of offspring”, in other words, it must be the type of sexual act inherently ordered toward procreation. Unnatural sexual acts do not consummate a marriage. Contracepted natural sexual acts do not consummate a marriage. If the couple have never had non-contracepted natural intercourse, then they do not have the full Sacrament of Marriage.
Do I also need to point out that contraception is intrinsically evil and always gravely immoral? So, too, are all unnatural sexual acts intrinsically evil and always gravely immoral. So in addition to not having a valid Sacrament of Marriage, they would also be committing many grave sins, by deliberately choosing sexual acts that are non-procreative.
Now some points of Canon Law are merely rules and regulations; they are judgments of the prudential order. But other Canons, particularly on the Sacraments, exercise the authority of the Church to such an extent that violating or failing to fulfill a Canon invalidates a Sacrament. For example, one of the Canons prohibits marriage to a second or third cousin without a dispensation. In the well-known case of New York City mayor Rudy Giuliani, he married his second cousin without a dispensation, and so his marriage was later annulled. It was not a valid Sacrament because a Canon was not fulfilled that pertains to the validity of marriage.
Similarly, in the Canon on the consummation of marriage, if the baptized man and woman have exchanged vows with proper consent, in a marriage ceremony with proper form, then their marriage is ratified, but not yet consummated. In order to consummate the marriage, they must have natural marital relations open to life. If they use contraception continuously, from the time of their vows and thereafter, then their marriage is not consummated. They in fact do not have a valid Sacrament of Marriage.
Is the Church compelled to annul this type of unconsummated marriage, if the couple request it? Yes. For the Church cannot compel anyone to have sexual relations. If they have decided to part from one another, and have never consummated the marriage, and they apply for an annulment, the Church cannot require them to remain together and to have marital relations. The Church must recognize the truth that their marriage was never consummated (if this truth is established before the Church as fact), and therefore the marriage does not have the unbreakable bond of the Sacrament.
On the other hand, the eternal moral law can sometimes require the couple to remain together and to have natural marital relations open to life. For they willingly exchanged vows before God, and marriage is ordered by its very nature toward procreation. They could obtain an annulment on the grounds of lack of consummation, but they would, in some cases, be sinning against God. For they would be capable, in some cases, of remaining together and of consummating their marriage. What the law permits or requires is one thing, but what the eternal moral law permits or requires is sometimes quite different.
A Catholic couple who have used contraception of any kind continuously since their wedding ceremony, so that they have never engaged, not even once, in natural marital relations open to life, do not have the valid Sacrament. And so their contracepted sexual acts are not only gravely immoral due to the deprivation of the procreative meaning in the moral object, these sexual acts are also gravely immoral due to a deprivation of the marital meaning. The couple have a marriage that is ratified only, and not yet validly consummated. And so their contracepted sexual acts are non-marital.
Suppose that a woman is using the birth control pill, while unmarried and not sexually active, to treat a medical disorder. If she continues to use the pill after exchanging vows, then all her sexual acts with her spouse are contracepted. For the medical purpose of taking the pill does not change the moral object from evil to good. The type of act deliberately chosen is contracepted sex. And so, even in this case, the couple have not validly consummated their marriage. Their contracepted sexual acts are a type of fornication as well as the sin of contraception. Every intrinsically evil act is immoral, due to the deliberate choice of an act that is inherently disordered, for such an act is, by its very nature, in and of itself, apart from the purpose for choosing the act, apart from all of the circumstances of the act, an evil act.
The choice of contracepted sex is intrinsically evil and always gravely immoral. Contracepted sexual acts do not consummate a marriage, and so the couple would remain without the bond of the Sacrament.
But what if the couple use natural family planning (NFP) continuously since exchanging vows? Is their marriage valid or invalid? The answer depends on an important point, concerning consent. NFP leaves the sexual act open to life, and so there is no question of a lack of openness to procreation. But Pope Pius XII, in his Address to Midwives, makes an interesting point concerning the possible misuse of NFP and the validity of the consent to marriage.
Pope Pius XII: “If one of the parties contracted marriage with the intention of limiting the matrimonial right itself, and not only its use, to the periods of sterility, in such a manner that, during the other days, the other party would not even have the right to ask for the debt, then this would imply an essential defect in matrimonial consent, which would result in the marriage being invalid, because the right deriving from the marriage contract is a permanent, uninterrupted, and continuous right of husband and wife with respect to each other.” (Address to Midwives, n. 35)
NFP is not intrinsically evil, because it does not deprive sexual acts of any of the three good moral objects required by God: the marital, unitive, and procreative meanings. However, NFP can still be misused, just as any good act might be misused. In particular, if one or both spouses intend to use NFP so strictly, and continuously, from the time of exchanging vows, so that neither spouse has the matrimonial right (the marriage debt) except during days of infertility, then the consent of the marriage has an essential defect, and the marriage is invalid.
So in both of the above types of cases, we see that natural marital relations open to life is an essential part of the Sacrament of Marriage. Defects that substantially affect this required element of marriage can invalidate the marriage. For the Sacrament is ordered primarily toward the procreation and education of children as its first purpose and highest good.