Dr. Janet Smith is a Catholic theologian and author of "Humanae Vitae: A Generation Later" and "Self-Gift: Essays on Humanae Vitae and the Thought of John Paul II." She has frequently written and spoken about Humanae Vitae, including in her signature talk, entitled "Contraception: Why Not".
Smith said the Catholic Church instead teaches that God has given humans reason and freedom to choose to have children freely, or to abstain when they are fertile.
"God gives us the possibility of pursuing many goods; he forbids us from doing evil, but permits us to choose freely between goods," Smith told CNA.
"Some couples are blessed with many resources both material and spiritual that enables them to have many children, but others need to limit their family size because of various difficulties in their lives. Certainly couples should be generous in their child-bearing, but the Church teaches that for serious or just reasons spouses may limit their family size," she said.
NFP differs from contraception by allowing the couples to fully participate in the marital embrace without removing the possibility of conceiving, Smith noted. The Church supports NFP because it does nothing to change the meaning of the marital act.
"Contraception undercuts that meaning since it removes the commitment-making power of procreation."
Church teaching also differs from the quiverfull mentality in that couples experiencing fertility are also free to attempt to remedy physical defects so that they may have children, Smith said.
"[I]f couples have correctable physical defects that prevent them from conceiving, it is fully in accord with God's will that they attempt to have those defects repaired," she said.
Pope Paul VI, for which the institute in Omaha is named, wrote one of the most oft-referenced encyclicals on the subject of marriage, sexuality and family planning in his encyclical letter, Humanae Vitae.
In it, Pope Paul VI first states that "the transmission of human life is a most serious role in which married people collaborate freely and responsibly with God the Creator. It has always been a source of great joy to them, even though it sometimes entails many difficulties and hardships."
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In section 10 of the letter, the pope states: "Married love, therefore, requires of husband and wife the full awareness of their obligations in the matter of responsible parenthood, which today, rightly enough, is much insisted upon, but which at the same time should be rightly understood."
Rightly understood, responsible parenthood is exercised "[w]ith regard to physical, economic, psychological and social conditions...by those who prudently and generously decide to have more children, and by those who, for serious reasons and with due respect to moral precepts, decide not to have additional children for either a certain or an indefinite period of time."
What serious reasons are serious enough?
Pope Paul VI wrote that while Catholic couples are free to exercise their reason and freedom in planning their families, they also must involve God in their decisions.
"[T]hey are not free to act as they choose in the service of transmitting life, as if it were wholly up to them to decide what is the right course to follow," he wrote. "On the contrary, they are bound to ensure that what they do corresponds to the will of God the Creator. The very nature of marriage and its use makes His will clear, while the constant teaching of the Church spells it out."
Smith said that there are a variety of serious reasons for which couples may decide to avoid having children for a time or an indefinite period, depending on the circumstances.