Objectively, certain thoughts, actions, and omissions entail grave sinful matter. As
Catholics, we are obliged to form our consciences regarding what constitutes grave matter in
accordance with the Church’s teaching. While it is not possible to make a complete list of
thoughts and actions that involve grave matter, they would all be serious violations of the law of
love of God and of neighbor. If we follow the order of the Ten Commandments, some examples
of such thoughts and actions would be:

• Believing in or honoring as divine anyone or anything other than the God of the Holy

• Swearing a false oath while invoking God as a witness

• Failing to worship God by missing Mass on Sundays and holy days of obligation.
without a serious reason, such as sickness or the absence of a priest.*  

• Acting in serious disobedience against proper authority; dishonoring one’s parents by
neglecting them in their need and infirmity.

• Committing murder, including abortion and euthanasia; harboring deliberate hatred of
others; sexual abuse of another, especially of a minor or vulnerable adult; physical or
verbal abuse of others that causes grave physical or psychological harm.

• Engaging in sexual activity outside the bonds of a valid marriage.**

• Stealing in a gravely injurious way, such as robbery, burglary, serious fraud, or other
immoral business practices

• Speaking maliciously or slandering people in a way that seriously undermines their
good name.

•  Producing, marketing, or indulging in pornography.

•  Engaging in envy that leads one to wish grave harm to someone else
Catholics who are conscious of committing any mortal sin must receive the Sacrament of
Penance before receiving Holy Communion. Assistance in examining one’s conscience is
available from confessors and spiritual directors.

*The Code of Canon Law obliges the faithful to participate in the Mass on each and every Sunday and holy day
of obligation (see CIC, c. 1247). Provided that the particular law of their Church sui iuris permits it, Eastern
Catholics may fulfill their obligation on these days by participating in the celebration of the divine praises (see
CCEO, c. 881 §1).

**For different reasons, some Catholics find themselves in a marriage that is recognized according to civil law,
but is not valid according to Church law. Each individual's subjective moral state may vary. Nonetheless,
persons in this situation should seek to have their marriage rectified according to the law of the Church so that
they may receive Holy Communion.