Everyone knows—or almost everyone does—that there are morally good actions and morally evil actions. But when is an action not only wrong, but sinful? And particularly mortally sinful? After all, as St. John says, “all wrongdoing is sin, but there is sin which is not mortal” just as “there is sin which is mortal” (1 John 5:16,17). A mortal sin is one that “destroys in us the charity without which eternal beatitude is impossible.

Unrepented, it brings eternal death,” as the Catechism of the Catholic Church (CCC) puts it (1874). That’s what makes it “mortal,” or deadly: it cuts us off from God forever, unless it is “redeemed by repentance and God’s forgiveness” (CCC 1861).  Thanks be to God, not every evil action is mortally sinful. So how do we know which is which? Just as there are three ingredients in evaluating a moral action (the object, intention, and circumstances), so there are three ingredients in a mortal sin: (1) “grave matter,” (2) “full knowledge,” and (3) “deliberate consent.” And the Catechism is clear that all “three conditions must together be met” (1857).