Listers, the “9 Ways of Being an Accessory to Another’s Sin” is taken from the 1962 Roman Missal under the heading of “The Most Necessary Prayers.” The list is commonly used as part of the Catholic’s examination of conscience before receiving the Eucharist. The list is simple, but a necessary guidepost for those striving after the Christ-centered life of virtue.

Accessory to Another’s Sin

I. By counsel
II. By command
III. By consent
IV. By provocation
V. By praise or flattery
VI. By concealment
VII. By partaking
VIII. By silence
IX. By defense of the ill done

The Holy See

Catechism of the Catholic Church

2504 "You shall not bear false witness against your neighbor" (Ex 20:16). Christ's disciples have "put on the new man, created after the likeness of God in true righteousness and holiness" (Eph 4:24).
2505 Truth or truthfulness is the virtue which consists in showing oneself true in deeds and truthful in words, and guarding against duplicity, dissimulation, and hypocrisy.
2506 The Christian is not to "be ashamed of testifying to our Lord" (2 Tim 1:8) in deed and word. Martyrdom is the supreme witness given to the truth of the faith.
2507 Respect for the reputation and honor of persons forbids all detraction and calumny in word or attitude.
2508 Lying consists in saying what is false with the intention of deceiving one's neighbor.
2509 An offense committed against the truth requires reparation.
2510 The golden rule helps one discern, in concrete situations, whether or not it would be appropriate to reveal the truth to someone who asks for it.
2511 "The sacramental seal is inviolable" (CIC, can. 983 § 1). Professional secrets must be kept. Confidences prejudicial to another are not to be divulged.
2512 Society has a right to information based on truth, freedom, and justice. One should practice moderation and discipline in the use of the social communications media.