On the Eighth Precept of the Decalogue

You shall not speak false testimony against your neighbor. Exod. xx, 16. - You shall not say false testimony. Matth. xix, 18

This precept, insofar as it is negative, prohibits chiefly and primarily that false testimony be said, both in judgment and outside judgment; indirectly and secondarily, that the reputation and honor of one's neighbor be injured. But insofar as it is affirmative, it commands, according to the Roman Catechism on the 8th precept, n. 2, "that, simulation and deceits having been removed, we measure our words and deeds by simple truth." Wherefore by this precept there is prohibited: 1st. perjury against one's neighbor; 2nd. lying; 3rd. detraction; 4th. contumely; 5th. rash judgment and injurious suspicion. Of each, except perjury, concerning which enough was said in the second precept, one must speak.