THE CATECHISM OF ST. PIUS X
The Sixth and Ninth Commandments
1 Q: What does the Sixth Commandment, Thou shalt not commit adultery, forbid?
A: The Sixth Commandment, Thou shalt not commit adultery, forbids every act, every look and every word contrary to chastity; it also forbids infidelity in marriage.
2 Q: What does the Ninth Commandment forbid?
A: The Ninth Commandment expressly forbids every desire contrary to that fidelity which husband and wife vowed to observe when contracting marriage; and it also forbids every guilty thought or desire of anything that is prohibited by the Sixth Commandment.
3 Q: Is impurity a great sin?
A: It is a most grave and abominable sin in the sight of God and man; it lowers man to the condition of the brute; it drags him into many other sins and vices; and it provokes the most terrible chastisements both in this world and in the next.
4 Q: Is every thought that comes into the mind against purity a sin?
A: The thoughts that come into the mind against purity are not of themselves sins, but rather temptations and incentives to sin.
5 Q: When is a bad thought a sin?
A: Bad thoughts, even though resulting in no bad deed, are sins when we culpably entertain them, or consent to them, or expose ourselves to the proximate danger of consenting to them.
6 Q: What do the Sixth and Ninth Commandments command?
A: The Sixth Commandment commands us to be chaste and modest in act, in look, in behavior, and in speech. The Ninth Commandment commands us in addition to this to be chaste and pure interiorly, that is, in mind and in heart.
7 Q: What must we do to observe the Sixth and Ninth Commandments?
A: To be able to observe the Sixth and Ninth Commandments, we ought to pray often and from our hearts to God; be devout to the Blessed Virgin, the Mother of purity; remember that God watches us; think on death, on the Divine chastisements, and on the Passion of Jesus Christ; guard the senses; practice Christian mortification; and frequent the Sacraments with the proper dispositions.
8 Q: What must we avoid in order to preserve ourselves chaste?
A: To preserve ourselves chaste we must shun idleness, bad companions, the reading of bad books and papers, intemperance, the sight of indecent statues or pictures, licentious theaters, dangerous conversations, and all other occasions of sin.