In light of the Obama Administration’s HHS Mandate on providing birth control, the question has been posed to me of why the Catholic Church regards birth control as gravely sinful. Using Pope Paul VI’s encyclical, Humanae Vitae (or Of Human Life in English!), it behooves me to make several points on the Church’s teaching on contraception and responsible parenthood. Humanae Vitae, 10 begins with the teaching on responsible parenthood, which each married couple is called to. This ‘responsible parenthood’ refers to the knowledge and respect for the biological functions and laws which are part of humanity. This includes dominion of the reason and will over the tendencies of instinct or passion. A couple exercises responsible parenthood by their decision to bring up a large family or, due to grave reasons, space or avoid conception. To fully exercise responsible parenthood, the couple must correctly recognize their duties towards God, each other, their family, and lastly towards society.
Avoiding Conception For Grave Reasons
Every conjugal act must remain open to the possibility of new life. However, for grave reasons, it may not be prudent for a couple to conceive. There are both licit and illicit ways to avoid conception. According to HV, 16, periodic continence (also referred to as Natural Family Planning) may be licitly used to avoid births, while the use of artificial birth control is gravely sinful. By practicing periodic continence, the couple does not violate the moral principles of making the conjugal act intentionally infertile. Both NFP and contraception seek to avoid births, but there is a fundamental difference. By practicing periodic continence, there is use of a natural disposition rather than dominance over nature and the body. Conception is not made impossible; it disappears on its own. In practicing NFP, the couple practices continence during the woman’s fertile period of the month. NFP assists love, in that the other person is worth waiting for. There is the virtue of self-mastery and respect for the body.
The Body Is The Person
Contraception on the other hand, violates moral principles. First off, either the sexual act or the sexual faculty is violated through sterilization or artificial contraception. Man does not have unlimited dominion over his body or fertility. The body is treated as sub-personal when man tries to exercise domination over it. This is a matter of injustice to both the individual and their spouse. 
As a woman, my fertility is not merely something I have, it is part of my being. The body is the person. According to John Paul II’s Theology of the Body, we are embodied souls… it is the body AND soul that make up the person. Secondly, contraception creates sexual lies. There is not a total self-gift, even though the body speaks of it. The spouse is withholding part of his or herself. The mentality of contraception says that procreation is not necessary to express love. It implies that sexual intercourse is good as long as it is satisfying. When the focus is taken off procreation, genital intercourse no longer is necessary and there are many acts which are instead considered sex. Pleasure oftentimes becomes the end, and the sexual act becomes counterfeit, as there is no longer the self-gift to the spouse. The Christian sense of the person is lost. The human heart fails to be satisfied by this mentality.
Domination Over The Body
The difference between NFP and contraception is not the effectiveness of spacing births. It is not the intention, because NFP can be misused, and those using contraception may genuinely have sincere and good intentions. In regards to being ‘natural’, contraception is not condemned because it employs science and NFP does not; rather NFP/PC is ‘natural’ because it respects the body. The fundamental difference is that contraception impedes a natural process and seeks domination of the body, which is the person. Periodic continence is the use of a natural disposition. There is no dominance, instead virtue and chastity are practiced, and love is fostered.
