Contraception deprives the sexual act of its procreative meaning, thereby causing the contracepted sexual act to be intrinsically evil and always gravely immoral. When a man and woman choose to deprive the sexual act of its procreative meaning, they are choosing to reject one of the inherent meanings of sexuality in the plan of God for human nature. This rejection is gravely immoral because “the moral order of sexuality involves such high values of human life that every direct violation of this order is objectively serious.” (Sacred Congregation for the Doctrine of the Faith, Persona Humana, X.)
Pope Paul VI: “The Church, nevertheless, in urging men to the observance of the precepts of the natural law, which it interprets by its constant doctrine, teaches that each and every marital act must of necessity retain its intrinsic relationship to the procreation of human life.” (Humanae Vitae, n. 11-12.)
The moral object of an act of natural marital relations is threefold: marital, unitive, procreative. The deprivation of any one or more of these three meanings from a sexual act causes the moral object to be evil, and the act to be intrinsically evil and always gravely immoral. Premarital sex is intrinsically evil because it is non-marital. Unnatural sexual acts are intrinsically evil because they are non-unitive and non-procreative. Contracepted acts of natural intercourse are intrinsically evil because they are non-procreative.
Pope Pius XI: “But no reason, however grave, may be put forward by which anything intrinsically against nature may become conformable to nature and morally good. Since, therefore, the conjugal act is destined primarily by nature for the begetting of children, those who, in exercising it, deliberately frustrate its natural power and purpose, sin against nature and commit a deed which is shameful and intrinsically vicious.” (Casti Connubii, n. 54.)
Contraception is intrinsically against the design for human nature chosen by God, whereby sexual relations is ordered toward procreation, through the union of man and woman in marriage. The deliberate deprivation of the procreative meaning from sexual relations is contrary to natural law, contrary to the definitive teaching of the Magisterium, and intrinsically immoral. (The phrase ‘intrinsically vicious’ is a translation of the Latin text ‘intrinsece inhonestum,’ which is perhaps better translated as ‘intrinsically immoral’.)
Pope John Paul II: “When couples, by means of recourse to contraception, separate these two meanings that God the Creator has inscribed in the being of man and woman and in the dynamism of their sexual communion, they act as arbiters of the divine plan and they manipulate and degrade human sexuality — and with it themselves and their married partner — by altering its value of total self-giving. Thus the innate language that expresses the total reciprocal self-giving of husband and wife is overlaid, through contraception, by an objectively contradictory language, namely, that of not giving oneself totally to the other. This leads not only to a positive refusal to be open to life but also to a falsification of the inner truth of conjugal love, which is called upon to give itself in personal totality.” (Familiaris Consortio, n. 32.)
The two meanings inscribed by God in the being of man and woman, for use only within marriage, are the unitive and procreative meanings. In order to be moral, each and every marital sexual act must be unitive and procreative. The use of contraception separates the unitive and procreative meanings, depriving the sexual act of a good intended by God in His divine plan. The use of contraception closes the sexual act to life, and is therefore immoral.
Pope John Paul II, writing about Pope Paul VI’s encyclical Humanae Vitae: “And he concluded by re-emphasizing that there must be excluded as intrinsically immoral ‘every action which, either in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible.’ ” (Familiaris Consortio, n. 32, quoting Humanae Vitae, n. 14.)
All contraceptive acts deliberately render the use of the sexual faculty non-procreative. Contraceptive acts done “in anticipation of the conjugal act” would include taking a contraceptive pill or applying a contraceptive barrier before sexual relations. Contraceptive acts done in the “accomplishment” of the sexual act would include the withdrawal method of contraception, and any inherently non-procreative sexual act (unnatural sexual acts). Contraceptive acts done “in the development of its [the conjugal act’s] natural consequences” would include methods that interfere with conception after intercourse, such as spermicides and pills that prevent ovulation.
Since the use of contraception is intrinsically evil, no intention and no circumstance can justify its use. Intrinsically evil are always immoral, even with good intentions, even in dire circumstances (Veritatis Splendor, n. 81). The use of contraception, even by married persons, is always gravely immoral.
Pope Paul VI: “From this it follows that they are not free to act as they choose in the service of transmitting life, as if it were wholly up to them to decide what is the right course to follow. On the contrary, they are bound to ensure that what they do corresponds to the will of God the Creator. The very nature of marriage and its use makes His will clear, while the constant teaching of the Church spells it out.” (Humanae Vitae, n. 10.)
The only moral sexual act is natural marital relations open to life. The use of contraception is an objective mortal sin because it closes the sexual act to life. The use of contraception with full knowledge that the act is gravely immoral, and with full deliberation, is an actual mortal sin.