Sixth and Ninth Commandments
1 Q. What does the sixth commandment prohibit?
A. The sixth commandment, Thou shalt not commit adultery, forbids every act, every look, and every word contrary to chastity; it forbids also unfaithfulness in marriage.
2 Q. What does the ninth commandment forbid?
A. The ninth commandment expressly forbids every desire contrary to the fidelity which husband and wife pledged themselves to observe at marriage; and it forbids also every thought or guilty desire of anything which is forbidden by the sixth commandment.
3 Q. Is impurity a great sin?
A. It is a most grievous and abominable sin in the sight of God and man; it lowers man to the condition of a brute; it drags him into many other sins and vices; and it brings about the most terrible punishments both in this world and in the next.
4 Q. Is every thought that comes to mind against purity a sin?
A. Thoughts that come into the mind against purity are not in themselves sins, but temptations and inducements to sin.
5 Q. When is an evil thought a sin?
A. Evil thoughts, though they give rise to no evil action, are sin when we culpably entertain them, or indulge them, or expose ourselves to the proximate danger of indulging them.
6 Q. What do the sixth and ninth commandments command?
A. The Sixth Commandment commands us to be chaste and modest in deed, in look, in conduct, and in speech. The ninth commandment further commands us to be chaste and pure inwardly, that is, in mind and heart.
7 Q. What must we do to observe the sixth and ninth commandments?
A. In order to observe the sixth and ninth commandments, we must pray often and heartily to God; be devoted to the Blessed Virgin, the Mother of purity; remember that God watches over us; think of death, divine punishments, and the Passion of Jesus Christ; watch over the senses; practice Christian mortification; and frequent the sacraments with due dispositions.
8 Q. What must we avoid in order to keep ourselves chaste?
A. To keep ourselves chaste we must avoid idleness, bad company, the reading of bad books and newspapers, intemperance, the viewing of indecent statues or pictures, licentious theaters, dangerous conversations, and all other occasions of sin.
Deadly sins vs. 6:
The Catechism lists six specific sins against chastity: 1) adultery, 2) masturbation, 3) fornication/homosexual fornication, 4) pornography, 5) prostitution, and 6) rape.... (and the use of means to prevent pregnancy; excluded from the prohibition are the natural methods approved by the Church to postpone a pregnancy for grave causes based on sexual abstinence in the fertile days of the woman).
Interrupting the sexual act to prevent conception is also a mortal sin.