Before exploring the Church’s prohibition against contraception, it is important to be clear about what contraception is. Contraception is defined as “any action which either before, at the moment of, or after sexual intercourse, is specifically intended to prevent procreation—whether as an end or as a means (Humanae Vitae, #14).”
From the very beginning the Church has understood that marriage is a Divine institution that is governed by the natural law and therefore she has never accepted the possibility of adapting or changing the “laws of marriage” to suit the particular trends of any age. While marriage contains a free subjective element, “I wish to marry this person,” that freedom to choose marriage must be rooted in the objective order by understanding and accepting the natural law governing marriage. It is this objective order that the Church has always promoted and defended for the good of those entering into the Sacrament of Holy Matrimony and for the good of society as a whole. (See HV, #4, 10‑12, 16).
The objective order in question is the purpose of marriage. The purpose of marriage has been defined as being two-fold — the good of the spouses and the procreation and education of children. Because of this two‑fold purpose of marriage, marriage and the marital act of sexual intercourse itself is said to be both “unitive” and “procreative.” “It is not good for man to be alone,” (Genesis 2:18), and “be fruitful and multiply,” (Genesis 1:28).
Sometimes a compromise is put forth that suggests that as long as a couple is open to the transmission of new life within the broader context of their marriage, they can licitly use contraception in order to regulate the birth of their children. The problem with this position is that it fails to appreciate the connection between the liturgical act of marriage and each act of sexual intercourse itself as a renewal of that covenant of Holy Matrimony. Each and every act of sexual intercourse between a man and his wife must authentically tell the truth about the promises they made on their wedding day, which includes the promise to lovingly accept children from God. This does not mean however that every act of sexual intercourse must intend or result in the conception of new human life, but it means that every act must be open to the possibility of life, or in other words, the act must not repudiate the possibility of conception.
The Church is not condemning the regulation of birth per se, but rather certain means of regulation, namely, those means which act against procreation in a marital act. “The regulation of births represents one of the aspects of responsible fatherhood and motherhood.
Legitimate intentions on the part of the spouses do not justify recourse to morally unacceptable means (for example, direct sterilization or contraception).” (Catechism of the Catholic Church, #2399. See also CCC #2367-2371).
In light of the advances in medical science and our knowledge of the human body and its biological processes, the Church wisely encourages couples to apply themselves intelligently to the natural functions of their bodies, particularly with regard to the rhythms of the female cycle of fertility (HV, #16). By making use of naturally infertile times a couple may pursue the unitive good of marriage while at the same time not acting against the procreative good (there is no act of repudiation against life here). This same knowledge which can be used to avoid pregnancy can also be used to help achieve pregnancy, and in some cases even help identify gynecological problems.
The Bead System of Fertility Awareness and numerous other natural family planning methods are in conformity with the objective moral criterion for regulating birth.