What is Mortal Sin (The Catholic Definition)

Sin is an act we commit (or fail to commit) that harms us or someone else in some way. More importantly, it hurts our relationship with God. Mortal sin is the complete severing of our relationship with God. It is so serious that we have essentially turned our back on God. As a result, unless the mortal sin is absolved through the sacrament of confession, we are in danger of losing our place in Heaven and the possibility of Hell is likely.

The Catechism of the Catholic Church defines sin in this way:

1849 Sin is an offense against reason, truth, and right conscience; it is failure in genuine love for God and neighbor caused by a perverse attachment to certain goods. It wounds the nature of man and injures human solidarity. It has been defined as "an utterance, a deed, or a desire contrary to the eternal law."

1850 Sin is an offense against God: "Against you, you alone, have I sinned, and done that which is evil in your sight." Sin sets itself against God's love for us and turns our hearts away from it. Like the first sin, it is disobedience, a revolt against God through the will to become "like gods," knowing and determining good and evil. Sin is thus "love of oneself even to contempt of God." In this proud self-exaltation, sin is diametrically opposed to the obedience of Jesus, which achieves our salvation.

1851 It is precisely in the Passion, when the mercy of Christ is about to vanquish it, that sin most clearly manifests its violence and its many forms: unbelief, murderous hatred, shunning and mockery by the leaders and the people, Pilate's cowardice and the cruelty of the soldiers, Judas' betrayal - so bitter to Jesus, Peter's denial and the disciples' flight. However, at the very hour of darkness, the hour of the prince of this world, the sacrifice of Christ secretly becomes the source from which the forgiveness of our sins will pour forth inexhaustibly.


In order for a sin to be considered mortal, 3 conditions must all be met:

  1. The sin must involve serious matter. Things like murder (including abortion), rape, sexual activity outside of marriage, hatred, sacrilege, and heresy are always serious. Other things life theft could be serious or not depending on the circumstances such as the amount involved, whether the victim of our theft would be greatly impacted by it, etc. This is where a well-formed conscience is important.
  2. We must have full knowledge that we are committing this sin and that it is a serious matter. In other words, you cannot commit a mortal sin by accident.
  3. We must give full and unencumbered consent to committing the action. Mortal sins are premeditated (if even for a brief second), thereby disregarding God’s love and deliberately breaking His law.

If any of these three conditions are not met, then the sin is in some way lessened, though that does not mean we shouldn’t worry about it. It is possible to commit a mortal sin against any of the 10 commandments, depending on the circumstances.

Though an action may not be serious, it could still be very damaging to our relationship with God. All sin causes harm to our soul, and we should always resolve to avoid it. Even small sins contribute to callousness toward evil that if left unchecked can consume us over time. Small sins make us more likely to commit big sins.

Mortal sin must always be confessed to a priest before our relationship with God can be restored. All sins, no matter how bad can always be forgiven if we are truly sorry for them. Mortal sins have a way of burdening us. We always have an uncomfortable feeling when we are carrying these sins around with us. This burden can be relieved though the sacrament of confession. If you have mortal sins on your soul, you should make every effort to get to confession as soon as possible. Most Catholic parishes offer confession at least once a week (usually on Saturday). Many offer it at other times as well. A good priest will usually be willing to make an appointment to hear your confession at other times as well.

The Catechism of the Catholic Church has this to say about mortal sin:

1855 Mortal sin destroys charity in the heart of man by a grave violation of God's law; it turns man away from God, who is his ultimate end and his beatitude, by preferring an inferior good to him.

Venial sin allows charity to subsist, even though it offends and wounds it.

1856 Mortal sin, by attacking the vital principle within us - that is, charity - necessitates a new initiative of God's mercy and a conversion of heart which is normally accomplished within the setting of the sacrament of reconciliation:


When the will sets itself upon something that is of its nature incompatible with the charity that orients man toward his ultimate end, then the sin is mortal by its very object . . . whether it contradicts the love of God, such as blasphemy or perjury, or the love of neighbor, such as homicide or adultery. . . . But when the sinner's will is set upon something that of its nature involves a disorder, but is not opposed to the love of God and neighbor, such as thoughtless chatter or immoderate laughter and the like, such sins are venial.

1857 For a sin to be mortal, three conditions must together be met: "Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent."

1858 Grave matter is specified by the Ten Commandments, corresponding to the answer of Jesus to the rich young man: "Do not kill, Do not commit adultery, Do not steal, Do not bear false witness, Do not defraud, Honor your father and your mother." The gravity of sins is more or less great: murder is graver than theft. One must also take into account who is wronged: violence against parents is in itself graver than violence against a stranger.

1859 Mortal sin requires full knowledge and complete consent. It presupposes knowledge of the sinful character of the act, of its opposition to God's law. It also implies a consent sufficiently deliberate to be a personal choice. Feigned ignorance and hardness of heart do not diminish, but rather increase, the voluntary character of a sin.

1860 Unintentional ignorance can diminish or even remove the imputability of a grave offense. But no one is deemed to be ignorant of the principles of the moral law, which are written in the conscience of every man. The promptings of feelings and passions can also diminish the voluntary and free character of the offense, as can external pressures or pathological disorders. Sin committed through malice, by deliberate choice of evil, is the gravest.

1861 Mortal sin is a radical possibility of human freedom, as is love itself. It results in the loss of charity and the privation of sanctifying grace, that is, of the state of grace. If it is not redeemed by repentance and God's forgiveness, it causes exclusion from Christ's kingdom and the eternal death of hell, for our freedom has the power to make choices for ever, with no turning back. However, although we can judge that an act is in itself a grave offense, we must entrust judgment of persons to the justice and mercy of God.

Other Articles You May Like:

A Thorough Catholic Examination of Conscience
How to Make a Good Catholic Confession
What is Venial Sin (The Catholic Definition)
The Act of Contrition
Top 10 Emotional Reasons People Don't Go to Confession (and Why You Should Consider it Anyway)
What Does it Mean to Mention Sins in "Number and Kind" in Confession