Well, no, certainly never wait for my outline. I just post my notes in case people want to compare what they got out of the chapter with what I got out of it. If there's discussion to be had, then just discuss.
Sure, there is an active part that can block memories. We see this most clearly in people who have experienced a traumatic event and have no recollection of it. The mind protects the person by blocking out the event, maybe a car crash or being assaulted, until such a time when the mind can deal with it. However, modern psychology shows, and I think it's correct, that the memory is only blocked out from the conscious mind and the subconscious mind (to use psychological terms) still has to deal with it which can cause other problems. So, in modern therapy, oftentimes the goal is to get the person's psyche strong enough to deal with these things, then gently bring the issue to the foreground where it can be dealt with. Is this the right approach? I dunno, but it illustrates that things can be blocked out of conscious memory - now, this is an active blocking, but it is not conscious, and your question is about conscious blocking.
It seems to me that as an act of will we can push memories out, to the back, oftentimes by filling our head with new memories. But I don't see an active
conscious way of forgetting. It doesn't mean there isn't one, but really throughout history men have studied how to remember better rather than how to forget better.... One problem is that to consciously forget at some level we need to remember the memory to tell ourselves to forget it, but in remembering we strengthen the memory which is the opposite of what we want to do.
On the other hand, in Catholic teaching in confession our sins are completely blotted out. So, when God forgives us, He, in a sense, does actively destroy His memory of our sin. But, He's God, we're not, so I dunno if that helps us much except in that we're created in His image, especially with regard to the soul, and memory is part of the soul. So, at first glance it seems it may be possible at some level.
So my opinion is, I don't know if we can actively and consciously forget a memory. With what we have read so far, and my own cursory knowledge, it doesn't seem impossible, but in practice it seems unlikely.
Also remember that it is "active" in the sense
it performs an action rather than being acted upon, not necessarily that we control that action. So, if we remember something that we do not want to, the memory is actively presenting it even if it is not acting according to our will. The passive part of memory is the fact that images are impressed upon it.
So your question really comes down to how much our will can direct our memory. Again, I dunno the answer to that, but it sure is an interesting question. For sure, our will has control over our thoughts - we can push things out and bring things forward, but as regards memory proper, it's unclear to me. We can will ourselves to remember stuff, but our mind has a mind of its own (heh) sometimes, so I don't know if our control of it can be improved. It seems doubtful to me...
Also interesting, to me at least, is when you talk about why we remember. You say the memory serves as a warning not to sin again, and that's true. The pain of the memory, if we have the right disposition towards it (aha, another scholastic term!) is not to enjoy it, but to feel pain from it - and that guilt and pain, though we have been forgiven, is a form of temporal punishment for the sin.
Of course in all of us who have sinned in ways that "feel good" or we derive enjoyment from, a memory of some sinful act will intrude upon us from time-to-time. In general, whether we feel pain or pleasure from it, we should push it out: in the case of pain, because we are forgiven - so we accept the pain we feel at that instant as temporal punishment, then push the thought away so we don't become scrupulous or lose faith; in the case of pleasure, because it is sinful - so we don't dwell on it and push it out.
Given a particular sin, it seems to me that whether we feel pain or pleasure from it often comes from our disposition towards the memory. If we have a (I can't think of a better term, so work with me) "sanctified" disposition, we react in horror. If we have a "worldly" disposition, we dwell upon it. So, it may be that the thing to do is if we feel an urge to dwell upon it, take that as a sign we can become more "sanctified". That does not mean become scrupulous or some nut. That means realize that we are still weak and have not completely overcome this particular temptation. It means we still have work to do: prayer, Sacraments, etc. And in many cases we will never have the correct disposition towards these thoughts because we are fallen creatures, so it will be a life-long battle. Even the Saints were assaulted in this manner. What makes them Saints is they didn't die in battle.
Unrelated, but a comment of my own, we see again how our actions affect our soul directly. We remember our actions in our memory, our memory is part of our soul. So here is another way our actions imprint themselves on our soul. Personally, I find it fascinating how our souls are affected by our actions. As a kid I remember wondering what the mechanism was by which our souls become affected by our actions, good and bad. With St. Thomas, we are able to see some of those mechanisms.
