GOD calls us to be holy and we can be holy through any vocation we're called to….

Nice blog and web!

I am constantly refreshed and renewed by such writting.

In short, please keep up the good work!

Yours in Christ, Graham

Aquinas does not attempt to give an exhaustive list of what these universal principles of law are, but understands at least the ten commandments to be included.

The Catechism of the Catholic Church in some sense affirms the same general principle: 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 Catechism, even less so than St. Thomas, does not state which principles of natural law are intended in this affirmation. While it surely does not intend to say that "no is deemed to be ignorant of" any precept that belongs in any way to natural law, it also surely means to say more than that no is ignorant of the first precept of natural law, "do good and avoid evil". It does not here give examples, either, as Aquinas gives the example of fornication.

Since this post was a follow up to the previous post talking about
sin that follow from "ignorance of universal principles of law," I assumed this context. Perhaps I should have stated it explicitly.

Ignorance of Particular Acts
Aquinas does not believe that one is always able to know in particular that a concrete act is objectively disordered. Hence one is not in every case gravely obliged to this knowledge, and in some cases may not be obliged at all. Aquinas several times gives the example (a rather odd one, though with a scriptural precedent for it) of a man who has sexual intercourse with a woman whom he honestly believes to be his wife.

The situation you are describing seems more like this latter type. For example, if I make fun of someone because it gives me pleasure, and don't realize that this act is likely to hurt him very badly, I commit an act that is objectively seriously disordered, and if done with full realization would be mortally sinful. Yet if the ignorance doesn't proceed from a total lack of consideration for that person, but from carelessness, it would seem to be venially sinful. (Since most cases of making fun of people don't hurt them gravely, there doesn't seem to be a general grave obligation to take particular care to notice whether it might cause great harm in a particular case.)

The same thing, I think, would apply to some cases of theft, lying, gluttony, sexual sins, etc.

In my own experience of sinning, one of the most common kinds of ignorance is when I know that there is something sinful about what I am doing, but I am not exactly sure if in this particular case that it is/ was mortal. It certainly seems that in the account that STA is giving here that I either have to say that my ignorance is invincible (which it almost certainly is not) or that I commit a mortal sin. This seems demand a clarity of thought that most human beings simply do not and cannot have.

I take it that your main point is the first one. Granted the Church's teaching that contraception is intrinsically wrong, then those who believe it is not are in a state of ignorance. However, if this ignorance is not their own fault–if it does not arise from their willful negligence to learn from reliable sources, or from a disordered attachment to their own ways of thinking–then it is invincible ignorance, and the acts done consequently are not done out of a culpable ignorance. There is a reason why I said "Let’s suppose that the ignorance is not invincible ignorance."

You may also have intended the second point. If the Church's teaching on contraception were erroneous, then those using contraception with a conviction that it is morally legitimate would not be acting out of ignorance, but out of true opinion or knowledge. However, since I follow the Church's teaching on this point, I assumed that those who are convinced that contraception is not wrong are in ignorance–either culpable or inculpable ignorance.

If it helps to consider the point of this post, one might replace "use artificial contraception" with "have an abortion", "kill a sickly relative who cannot enjoy life anymore," "torture someone for the sake of vengeance", or something similar. Any of these could in principle be done with a conviction that the act is morally justified, and this mistaken conviction would either be inculpable/invincible, or culpable (the case I take up in this post).