What constitutes a mortal sin?

[jonnyws]

Is a mortal sin simply any act that the participent knows is sinful and commits anyway or does it have to be in breach of the ten commandments explicitly to count as mortal sin.

 

[mommyof4]

It has to be “grave matter.” Not just any old sin.

 

[jonnyws]

And a grave matter is defined as?

Sorry for the questions but I’m being prepared from adult acceptance into the church and we haven’t covered this bit yet; but it is bothering me.

 

[mommyof4]

Here’s a bit more info:

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."[131]

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.”[132] 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[133] 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.

 

[jonnyws]

Thanks, much clearer.

 

[fix]

In adition to the CCC you may check new advent:

For a deliberate mortal sin there must be full advertence on the part of the intellect and full consent on the part of the will in a grave matter. An involuntary transgression of the law even in a grave matter is not a formal but a material sin. The gravity of the matter is judged from the teaching of Scripture, the definitions of councils and popes, and also from reason. Those sins are judged to be mortal which contain in themselves some grave disorder in regard to God, our neighbour, ourselves, or society. Some sins admit of no lightness of matter, as for example, blasphemy, hatred of God; they are always mortal (ex toto genere suo), unless rendered venial by want of full advertence on the part of the intellect or full consent on the part of the will. Other sins admit lightness of matter: they are grave sins (ex genere suo) in as much as their matter in itself is sufficient to constitute a grave sin without the addition of any other matter, but is of such a nature that in a given case, owing to its smallness, the sin may be venial, e.g. theft.

 

[davidv]

Check out the definition of sin here:
newadvent.org/cathen/14004b.htm