**More than a couple of points but important nevertheless: **
**Where in the encyclical Casti Connubii does Pope Pius
mention any kind of specific birth control? **
The focus is on the intentions of the married couple on having children, primary end. Pope Pius XI ends the encyclical by stating the example of Onan as an evil use of man’s free will.
Genesis 38:8-10
8 Juda, therefore said to Onan his son: Go in to thy brother’s wife and marry her, that thou mayst raise seed to thy brother. 9 He knowing that the children should not be his, when he went in to his brother’s wife, spilled his seed upon the ground, lest children should be born in his brother’s name. 10 And therefore the Lord slew him, because he did a detestable thing.
St. Jerome’s exegesis is, "Onan who was slain because he grudged his brother seed. Does he imagine that we approve of any sexual intercourse except for the procreation of children?
St Augustine:
De Nuptiis et Concupiscentia #15, “It is, however,* one thing for married persons to have intercourse only for the wish to beget children, which is not sinful: it is another thing for them to desire carnal pleasure in cohabitation, but with the spouse only, which involves venial sin. For although propagation of offspring is not the motive of the intercourse, there is still no attempt to prevent such propagation, either by wrong desire or evil appliance.* They who resort to these, although called by the name of spouses, are really not such; they retain no vestige of true matrimony, but pretend the honorable designation as a cloak for criminal conduct. Having also proceeded so far, they are betrayed into exposing their children, which are born against their will. They hate to nourish and retain those whom they were afraid they would beget. This infliction of cruelty on their offspring so reluctantly begotten, unmasks the sin which they had practiced in darkness, and drags it clearly into the light of day. The open cruelty reproves the concealed sin.”
**St Thomas Aquinas Summa Theologica :
**
Suppl.Q.49,a.2, “One of these is required on the part of the agent and is the intention of the due end, and thus the offspring is accounted a good of matrimony”(
newadvent.org/summa/5049.htm)
Suppl. Q.49,a.3, “Secondly, faith and offspring may be considered as in their principles, so that offspring denote the intention of having children, and faith the duty of remaining faithful, and there can be no matrimony without these also, since they are caused in matrimony by the marriage compact itself, so that if
anything contrary to these were expressed in the consent which makes a marriage, the marriage would be invalid.”(
newadvent.org/summa/5049.htm)
Suppl. Q.41,a.4, Since no act proceeding from a deliberate will is indifferent, as stated in the Second Book (Sent. ii, D, 40, 1, 3; I-II, 18, 9), the
marriage act is always either sinful or meritorious in one who is in a state of grace. For if the motive for the marriage act be a virtue, whether of justice that they may render the debt, or of religion, that they may beget children for the worship of God, it is meritorious. But if the motive be lust, yet not excluding the marriage blessings, namely that he would by no means be willing to go to another woman, it is a venial sin; while if he exclude the marriage blessings, so as to be disposed to act in like manner with any woman, it is a mortal sin. And nature cannot move without being either directed by reason, and thus it will be an act of virtue, or not so directed, and then it will be an act of lust.(
newadvent.org/summa/5041.htm)
Please remember these are from very important ‘
Saints’.
GOD Bless.