"The Church has always taught the intrinsic evil of contraception, that is, of every marital act intentionally rendered unfruitful. This teaching is to be held as definitive and irreformable. Contraception is gravely opposed to marital chastity; it is contrary to the good of the transmission of life (the procreative aspect of matrimony), and to the reciprocal self-giving of the spouses (the unitive aspect of matrimony); it harms true love and denies the sovereign role of God in the transmission of human life. A specific and more serious moral evil is present in the use of means which have an abortive effect, impeding the implantation of the embryo which has just been fertilized or even causing its expulsion in an early stage of pregnancy. However, profoundly different from any contraceptive practice is the behavior of married couples, who, always remaining fundamentally open to the gift of life, live their intimacy only in the unfruitful periods, when they are led to this course by serious motives of responsible parenthood. This is true both from the anthropological and moral points of view, because it is rooted in a different conception of the person and of sexuality. The witness of couples who for years have lived in harmony with the plan of the Creator, and who, for proportionately serious reasons, licitly use the methods rightly called "natural," confirms that it is possible for spouses to live the demands of chastity and of married life with common accord and full self-giving."