1. In the Encyclical "Humanae vitae" we read: "The Church, in urging men to the observance of the precepts of the natural law, which it interprets by its constant doctrine, teaches as absolutely required that in any use whatever of marriage there must be no impairment of its natural capacity to procreate human life" (HV 11).
La norma moral de la Encíclica Humanae vitaesobre el acto matrimonial 1. En la Encíclica Humanae vitae leemos: "Al exigir que los hombres observen las normas de la ley natural, interpretada por su constante doctrina, la Iglesia enseña que cualquier acto matrimonial debe quedar abierto a la transmisión de la vida" (Humanae vitae, 11).