What Exactly is a Mortal Sin?

by Michael Shackleton · June 20, 2017

I confessed my sins to a priest and somehow I used the term “mortal sin” at the conclusion. To my surprise, the priest commented that he hadn’t heard me confess any mortal sins. Now I am confused. I learnt in catechism that breaking one of the Ten Commandments was a mortal sin and I could not have Communion unless I confessed it. Either I misunderstood the priest or Catholic doctrine has undergone some changes over the last 50 years, or I completely misunderstood my catechism teacher. I would appreciate some guidance. Tony

You have heard of the legal term “malice aforethought”. It generally refers to cases of murder. It means that the killer deliberately planned to kill someone. Another word used for this is “premeditated”.

Someone who does this malicious act can be found guilty of murder in a court of law. In moral theology they are said to have committed a mortal sin. The act fulfils the three conditions for mortal sin: grave matter, full knowledge and deliberate consent (Catechism of the Catholic Church 1857).

Catholic doctrine has regularly maintained that there is no mortal sin unless these three conditions are present.

A mortal sin consists in an act of grave matter, which is an offence against the Commandments, such as murder, adultery and blasphemy.

If you kill someone by accident in a car crash or in attempting to defend your property, there may be grave matter there but it is not clear that there is full knowledge and full consent.

Maybe this is what the priest was trying to tell you in the confessional. We cannot always swear that our sins were done with full awareness and evil intent. Confusion, ignorance, emotional states: things like these can influence our mind and will. What may be objectively wrong is not always subjectively wrong, because our conscience may not be certain that we are culpable.

In any case, we should shift the focus from sinfulness to the words of Christ who said: “If you love me you will keep my commandments” (Jn 14;15). We must concentrate on the bond of love between ourselves and our loving Father who “so loved the world that he gave his only Son” (Jn 3:16).

Mortal sin is called mortal because it kills that precious bond of love. Those whose conscience reproaches them that they have with malice aforethought dealt a mortal blow to their soul, are required to repent and confess their sin humbly and receive Christ’s and the Church’s warm welcome back.

Venial sins are less grievous as they do not mortally wound the soul, but they must be repented too in order for us to abide in the powerful love that binds us together with Christ and his Church.