Does anybody know where and when the widespread use of the distinction between objective and subjective sin was introduced? I can find plenty of medieval and modern distinction between perfect and imperfect acts, and between human and non-human acts. For instance, there is a lot on how somebody who sleeps with another's wife does not commit adultery if he does not know that she is married to another. But I can't find anything about how someone who knowing sleeps with another's wife might not really be committing adultery. There has to be something in the literature. I have seen several statements like "The Church teaches that adultery is objectively wrong, but not always subjectively sinful." I can see why it might not be sinful if it is not formally adultery, but I don't think that this is what they are saying.
I've looked around a bit in different descriptions of why we shouldn't judge others. There are obvious remarks on how it is not our place, how we lack the relevant knowledge, etc. It is like one servant judging another. There is also material on how we might not know circumstances that would mitigate or change the act. But most medieval and early modern authors seem to assume that if someone knowingly murders or commits adultery, we can know that they sinned mortally. Augustine states that we should then reflect on the fact that they might repent, and we might be damned, etc. The general approach seems to involve a combination of some of at least four elements: 1) don't judge if you don't need to because it is not your place, 2) you cannot know all the relevant circumstances, especially of acts that are not intrinsically evil, 3) even if you know that the neighbor's act is mortally sinful, you don't know if it is merely on account of weakness or ignorance instead of malice, and 4) you don't know that the person will repent and become a great saint, whereas you might be damned. I don't find any suggestions that we should consider that our neighbor is not in fact sinning by committing adultery, blasphemy, or murder. In other words, nobody says, "You can know that your neighbor is choosing to commit objectively evil actions such as murder or blasphemy, but you can't know that he is subjectively guilty." Where does this come from historically? Please send an e-mail or comment if you have citations from before the twentieth century that don't have to do with the formal/material distinction, or even if you know of anything that suggests the possibility of invincible ignorance concerning the substance of the Ten Commandments.