[Hermann the Cherusker]

However, it's important to remember that the Church says that abstinence may be used to avoid conception only for "grave reasons" or "serious motives."

Actually, the words used by the Sacred Penitentiary in the 19th century under Bl. Pius IX and Leo XIII, and by recent teachings of Paul VI and John Paul II in the 20th century use the words "just reasons" (see the Catechism, #2346). The words: "grave reasons" appears only in Pius XII's allocution.

[Tax-chick]

Thanks for the correction - I was paraphrasing from memory, rather than looking up the documents at the time. (I also had a disaster involving a baby, a bowl of cereal, and a diaper, right in the middle of posting.)