When is something a mortal sin?

[Larquetta]

I’ve had a difficult time grasping the concept of mortal sin. There are some times when I’m not sure if I or others have committed mortal sins. Here are a couple of examples.
Scenario #1: Someone isn’t sure if something is a sin or not, so he does it anyway and later finds out that it counted as grave matter.
Scenario #2: Someone isn’t Catholic and doesn’t believe in sin, but she is educated on Church teaching. She commits a sin which she knows the Church would consider grave matter but which she believes to be morally acceptable.
Scenario #3: Someone knows that what he’s doing isn’t moral, but he has no idea that it’s a serious sin.
Scenario #4: Someone frequently has sinful thoughts (examples would be jealous, angry, or lustful thoughts) but tries to push them from her mind

Which one(s) of these would count as mortal sins?

 

[TK421]

I’ve had a difficult time grasping the concept of mortal sin. There are some times when I’m not sure if I or others have committed mortal sins. Here are a couple of examples.
Scenario #1: Someone isn’t sure if something is a sin or not, so he does it anyway and later finds out that it counted as grave matter.
Scenario #2: Someone isn’t Catholic and doesn’t believe in sin, but she is educated on Church teaching. She commits a sin which she knows the Church would consider grave matter but which she believes to be morally acceptable.
Scenario #3: Someone knows that what he’s doing isn’t moral, but he has no idea that it’s a serious sin.
Scenario #4: Someone frequently has sinful thoughts (examples would be jealous, angry, or lustful thoughts) but tries to push them from her mind

Which one(s) of these would count as mortal sins?

Scenarios 1, 2, and 3 may or may not be mortal sins, depending on the soul and the amount of light they’ve received.

Scenario 4 is virtuous and meritorious.

 

[joeybaggz]

You really need to ask this question of a priest in confession. He is the best person to guide you.
My opinion, for what it is worth, none of the four is a mortal sin. Mortal sin requires a clear understanding of what is and is not grave matter, and willingness to carry it though. Mortal sin requires grave matter, sufficient reflection or understanding of the grave nature of the action before God, and a willingness without coercion to commit the act (full consent of the will). I don’t see all three in any of the above scenarios you post.