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 Scriptures • 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.