Do you mean objectively grave matter?
This is the point many people miss, and it’s important. I don’t think that most people on this thread are trying to debate that living in an invalid marriage is objectively
grave matter. It is.
But
mortal sin requires two additional conditions to be met.
So, while you can say living in an invalid marriage is objectively grave matter, you can’t say it’s a mortal sin unless you know 100% for certain what goes on in the heart, soul, and intellect of the specific people involved. For some it might be, for others it might not. But the bottom line is
you don’t know.
Words matter. I think if the OP
@HomeschoolDad were throwing around the term “objectively grave matter” rather than “objective mortal sin,” this thread would have gone slightly differently (only slightly, though, as I’m still not quite sure how it’s helping him achieve his goal).
Whether one realizes it or not or intends it or not, telling people they are in
objective mortal sin is judging them. Some would argue that even a person himself doesn’t know for sure if he is in a state of grace or not. When St. Joan of Arc was being interrogated at her trial, they asked her if she was in a state of grace. They did this because she would condemn herself either way. If she said no, she would admit to being out of God’s friendship. If she said yes, she would be presuming to know what God knows, which would be presumptuous. But she gave the “correct“ answer, saying “If I am not in a state of grace, may God put me there. If I am in a state of grace, may God so keep me.”