The Catholic Sacrament of Marriage is “ratum tantum” (ratified only) after the exchange of vows in the wedding ceremony, and is “ratum et consummatum” (ratified and consummated) after the spouses have had marital relations. The sexual relations in question is marital because the marriage begins with its ratification at the consent of the couple (the vows).
Due to the prevalence of grave sin among believing and practicing Catholics, the question arises: Which sexual acts are sufficient to constitute a consummation of the Sacrament?
“Can. 1061 §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.”
The couple are called spouses, even before the consummating act. That act is described in Canon law as meeting certain conditions. This part of the Canon clearly implies that other sexual acts, not fitting the description in the law, do not consummate the marriage. Thus, not any sexual act suffices.
The sexual act must be performed in a human fashion; this excludes any unnatural sexual acts, as well as artificial procreation. The act of consummation must be “suitable in itself for the procreation of offspring”, meaning that the act must be both the natural type of sexual act and it must not be a contracepted sexual act. Contracepted natural intercourse is not suitable in itself for procreation. A contracepted sexual act might result in procreation, accidentally. But it is not, in itself, ordered toward procreation.
Notice that the required act is not only procreative (“the procreation of offspring”), but also marital and unitive (“the spouses become one flesh”). The only sexual act that consummates a marriage is natural marital relations open to life, an act that is marital, unitive, and procreative. A sexual act open to life performed prior to the marriage vows is not marital. A contracepted sexual act is not procreative. An unnatural sexual act is neither procreative, nor truly unitive or marital.
Now let’s ask a related question: Is this requirement an essential part of the Sacrament, or a condition added by the Church? For the Church can add or subtract — to a limited extent — conditions for a Sacrament to be valid. But certain conditions are inherent to the Sacrament for its validity, as arising from the very nature of the Sacrament itself, and therefore such conditions cannot be changed by the Church.
Since marriage is, by its very nature, ordered toward the procreation and education of children, consummation is essential to the fullness of the Sacrament. And that is why a Sacrament of Marriage, which is ratified only, can be dissolved — either by the authority of the Holy See or by the taking of religious vows by either spouse. Moreover, children are procreated, in a human fashion, only by a certain type of sexual act, which is termed natural intercourse. Unnatural sexual acts, even when performed by a man and woman married to each other, are not ordered toward procreation, and so these acts are not marital, nor procreative, nor unitive. Artificial procreation is not an act in the human fashion, but after the manner of science and technology.
The natural sexual act alone is naturally and inherently ordered toward procreation. Therefore, natural intercourse is the only sexual act that can consummate a marriage, and it can do so only when it is not thwarted in its procreative end by the choice of any form of contraception. And since marriage, in and of itself, is primarily ordered toward procreation, this requirement cannot be changed by the Church. It is an essential requirement for any Sacrament of Marriage to be consummated.
Can infertile spouses consummate their marriage by natural marital relations open to life? Yes, they can. For they have not chosen to thwart the procreative meaning of marriage within the very act that should be an essential part of the Sacrament, consummation. The act chosen by the spouses, natural marital relations open to life, retains that proper ordering, even though it cannot attain the end toward which it is ordered. For it is not the attainment of the moral object that makes an act inherently good (or inherently evil), but rather the deliberate knowing choice of an act with a certain ordering, whether toward a good end or an evil one.
 Hardon, S.J., John. “Consummated Marriage”. Pocket Catholic Dictionary. Image Books. p. 91.
 E. Christian Brugger, Zenit.org, “More on Marriage and Contraception”.
 Ronald L. Conte Jr., Does Contracepted Sex Consummate a Marriage?
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