This coming July, we will mark the 50th anniversary of Pope Paul VI’s deeply controversial encyclical letter Humanae Vitae. I won’t bore you with the details of the innumerable battles, disagreements and ecclesial crises that followed upon this text. Suffice it to say that this short, pithily argued letter became a watershed in the post-conciliar Catholic Church and one of the most significant points of contention between liberals and conservatives. Its fundamental contention is that the moral integrity of the sexual act is a function of the coming together of its “procreative and unitive” dimensions. That is to say, sexual intercourse is ethically upright only in the measure that it is expressive of love between married partners and remains open to the conception of a child. When, through a conscious choice, the partners introduce an artificial block to procreation — when, in a word, they separate the unitive and procreative finalities of the sexual act — they do something which is contrary to God’s will.