CCC 2486
Life in Christ›SECTION TWO THE TEN COMMANDMENTS›CHAPTER TWO YOU SHALL LOVE YOUR NEIGHBOR AS YOURSELF›III. Offenses Against Truth
Since it violates the virtue of truthfulness, a lie does real violence to another. It affects his ability to know, which is a condition of every judgment and decision. It contains the seed of discord and all consequent evils. Lying is destructive of society; it undermines trust among men and tears apart the fabric of social relationships.