It's important to distinguish between various types of heresy, because the "type" of heresy determines the punishment of the heretic, his guilt before God and his relationship to the Church. All formal heresy, which is when a person knows that the Catholic Church teaches X and the person chooses to deny or doubt X, is a mortal sin. If such heresy is public, then in addition to the mortal sin one is no longer a member of the Church. Material heretics dissent from what the Church teaches, but they are unaware that they're supposed to believe what the Church teaches-- such a heretic is not guilty of heresy before God, however if he is a public heretic, he is not a member of the Church.
Private heresy does not sever one's membership in the Church.
Are these distinctions to be found in dogmatic theology (I just purchased Van Noort!) or the Code of Canon Law or both?
Can you suggest which commentary on the old Code of Canon Law is best for use by a layman?
The distinction between formal and material properly belongs to moral theology. Though modern writers tend to explain this without the sort of precision that one would like to see. Of course, I am "stuck" with English-only sources, perhaps works in other languages do a better job. I think that De Lugo is probably the best source available, thanks to a translation by J.S. Daly:
http://strobertbellarmine.net/forums/viewtopic.php?f=11&t=1632&sid=34bd18f3efaca7ecb7013b109d8ce926That's not to say that the modern authorities are useless, but just that they oftentimes imply or even outright state that Catholics can be material heretics.
As far as public vs. occult, that pertains more to dogmatic theology and canon law. Do you have Van Noort yet? You'll want to read his chapter on membership, which is probably the best synopsis on the issue I've read. Vol II, starting on page 236. If you haven't received yours yet, you can read a scan of the chapter here:
http://www.scribd.com/doc/224429380/Van-Noort-Vol-2-Members-of-the-ChurchAt the turn of the last century, there was an impulse to make theology more accessible to the laity, so there are manuals written in mind for laymen of varying levels of intellect and free time. However, this pressure never occurred in canon law, and as such canon law manuals are always written with the seminarian in mind. And since law is law, and precision, definitions and terminology is everything (not to say it is unimportant in these other fields) there is no way to really "dumb it down." Doesn't mean a good handle can't be had on it. I only own two proper commentaries, and Penny Catechism quoted from both of them.
I would recommend Bouscaren and Ellis to start. Pros: Easily and intuitively formatted, easy to find what you're looking for, few "over-explanations," comfortable size, good typeface with appropriate bolding and organization, and best of all you can find a copy for probably twenty USD with shipping. Maybe even cheaper if you hold out a bit.
Cons: Because they avoid over-explaining things, there is a tendency to under-explain them. Not all of the canons are treated, most notably they do not comment on canon 882, which is a shame. It's by no means a short book, but in the scheme of things it's definitely brief. Of course, this is probably what makes it a good intro book.
Woywood is far more comprehensive, though there are a few things I dislike which would keep me from recommending as a first commentary.
(BTW-- Woywood has a "practical commentary" on the Code, and then he has another commentary. I speak of the "practical commentary" and don't know much about the other. The reason I bought the "Practical Commentary" is that it's the "Practical commentary" that I always find cited as a source. So, when I refer to Woywood, I am referring to his "Practical Commentary")
There are two ways you can buy Woywood, both with their own pros and cons. One way is to buy the two volume version. Pros are that it's easier to read because it's not as big. Don't underestimate the physical size of a book when considering between different versions! You're the one who'll be sitting there reading it for hours. Now, I have not actually used a two volume set but have a friend who owns them and I can tell you that I would much prefer to read out of those rather than the condensed one volume. As to the content, it's substantially the same-- though I'm not sure about the index in the two volume set. One drawback with the two volume set is cost. You'll be lucky to get the set for less than fifty USD. That might not be a problem for you, but the cost of these books can add up quickly.
A cheaper alternative is getting the Practical Commentary in the 1957 edition which was revised by a Callixtus Smith. It's both volumes put into one book. The main downside to this is that it's pretty big. While it's far more comprehensive than Bouscaren, I find that it is not well organized. The index is comprehensive enough (it really is a great index) but it's very confusing because there are page numbers, canon numbers, and then PARAGRAPH numbers. Not to mention that because there are two volumes in one (plus appendix) the page numbers "start over" with the next volume, and I think they might even start over again for the appendices.
I think it's gratuitous to use paragraph numbers in a canon law book. The canons are numbered for a reason! Adding paragraph numbers just needlessly confuses things. Anyways, it's quite comprehensive and better yet, because it is a later edition it keeps in mind any changes to the law-- and there are changes. So for this reason, it is quite valuable, being the latest edition of a commentary on the 1917 by a tradition author available in English. The appendices are quite helpful as well. I was able to get the 1957 edition for around 30 USD including shipping.
What is also a tremendous resource, and FREE(!!!) is Augustine's commentary on the code. It is the oldest of the three, but it is definitely worth it's weight. Eight Volumes all available on archive.org for free. Incidentally, the eight volume set is not too expensive. I've done the math and if you play your cards right, you could end up paying about 15 USD per volume, and could probably get the set for less than 150 USD (that is, assuming you bought them one at a time).
Here is a link:
https://archive.org/details/1917CodeOfCanonLawCommentaryThere is also Abbo and Hannan, though I do not own them and have not used them. I've heard good things, though their commentary is even more expensive than Woywood's. And there are various other brief manuals. Once you get started, what you'll probably find more interesting than anything else are the various CUA dissertations for the D.C.L. degree. They are highly detailed dissertations on just a single canon, with historical synopsis. A few of these are available online for free. And depending on the one you want, they can typically be found for less than twenty dollars a volume.
Final note: Keep in mind that at least for the English commentaries, the code itself is not in the commentary. With Augustine, he gives it in Latin. Neither Bouscaren or Woywood consistently give the exact wording for each law, though they will for some. If you want the law itself in English, you will need to buy Dr. Peters translation. You'll spend 30-40 USD on that. Odd as it may sound, I do not think it's necessary, only helpful to have the actual code in English.