Humanae Vitae is online at the Vatican site, and the text highlighted below is © Copyright – Libreria Editrice Vaticana.
This section summarizes those that preceded, and gives Church teaching on contraception and sterilization in strong terms:
14. Therefore We base Our words on the first principles of a human and Christian doctrine of marriage when We are obliged once more to declare that the direct interruption of the generative process already begun and, above all, all direct abortion, even for therapeutic reasons, are to be absolutely excluded as lawful means of regulating the number of children.* Equally to be condemned, as the magisterium of the Church has affirmed on many occasions, is direct sterilization, whether of the man or of the woman, whether permanent or temporary.** Similarly excluded is 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.*** Neither is it valid to argue, as a justification for sexual intercourse which is deliberately contraceptive, that a lesser evil is to be preferred to a greater one, or that such intercourse would merge with procreative acts of past and future to form a single entity, and so be qualified by exactly the same moral goodness as these. Though it is true that sometimes it is lawful to tolerate a lesser moral evil in order to avoid a greater evil or in order to promote a greater good,” it is never lawful, even for the gravest reasons, to do evil that good may come of it (See Rom 3. 8)—in other words, to intend directly something which of its very nature contradicts the moral order, and which must therefore be judged unworthy of (people), even though the intention is to protect or promote the welfare of an individual, of a family or of society in general. Consequently, it is a serious error to think that a whole married life of otherwise normal relations can justify sexual intercourse which is deliberately contraceptive and so intrinsically wrong.
* See Council of Trent Roman Catechism, Part II, ch. 8; Pius XI, Casti connubii: AAS 22 (1930), 562-564; Pius XII, Address to Medico-Biological Union of St. Luke: Discorsi e radiomessaggi, VI, 191-192; Address to Midwives: AAS 43 (1951), 842-843; Address to Family Campaign and other family associations: AAS 43 (1951), 857-859; John XXIII, encyc. letter Pacem in Terris: AAS 55 (1963), 259-260 [TPS IX, 15-16]; Gaudium et Spes 51.
** See Pius XI, Casti connubii: AAS 22 (1930), 565; Decree of the Holy Office, Feb. 22, 1940: AAS 32 (1940), 73; Pius XII, Address to Midwives: AAS 43(1951), 843-844; to the Society of Hematology: AAS 50 (1958), 734-735 [TPS VI, 394-395].
*** See Council of Trent Roman Catechism, Part II, ch. 8; Pius XI, Casti connubii: AAS 22 (1930), 559-561; Pius XII, Address to Midwives: AAS 43 (1951), 843; to the Society of Hematology: AAS 50 (1958), 734-735 [TPS VI, 394-395]; John XXIII, Mater et Magistra: AAS 53 (1961), 447 [TPS VII, 331].