According to Western Christianity, actual sin, as distinguished from original sin, is an act contrary to the will and law of God whether by doing evil (sin of commission) or refraining from doing good (sin of omission). It can be either "mortal" or "venial".
Catholic hamartiology is a branch of Catholic thought that studies sin. According to the Catholic Church, sin is an "utterance, deed, or desire", caused by concupiscence, that offends God, reason, truth, and conscience. The church believes sin is the greatest evil and has the worst consequences for the sinner (original sin and damnation), the world (human misery and environmental destruction), and the Catholic Church itself (Passion of Jesus and wounds to the church's unity). Based on the Bible, the Catholic Church distinguishes between two kinds of sins: mortal sin and venial sin. The Catholic Church also distinguishes between the state of being in original sin and the commission of actual sin.