But that would seem to imply that, for example, the RIAA can't sue someone for downloading half a song (or all but the last 5 seconds).
If anyone is tempted to start spinning the English meaning of the term "collected" to point out how in some sense a song is often a collection of a lot of other elements that may be further copyrighted, stop. The English meaning is not the relevant one, the legal meaning is. A single song is not, legally, a collected work, it is a single work.
If anyone is tempted to construct some exceptional song-like thing that is also a collected work, yes, very good, you've got your thesis topic for your copyright class all laid out, but it is an exception, not the rule.
Also, for the record, that wasn't the question I was trying to forestall with my last paragraph. I was more after someone doing something bizarre like creating a multi-hour "song" where each "instrument" is a full other song loaded as one big sample or something. Generally speaking the answer to this sort of trickery is "You're a programmer, and you're using thought processes designed to slip things past computers. Judges are human." There are certainly ways to "slip things past" a human judge as well, but they are very different. Human judges generally react poorly to outright sophistry, where computers don't mind it one bit.
If copying individual elements (all the chapter titles) of a work is fine, how is it that it is unacceptable to make an original song that contains a 5 second sample of a single instrument from another song? Both are copying a very small excerpt from a larger work.
From my point of view, your question is odd because you've made up both parts of the if clause from whole cloth. Copying "individual elements" may or may not be fine, and five second samples are just plain irrelevant to the discussion being had.
Again, "collective work" is an important term here. It is not clear to me that you understand what that means, and generally trying to answer questions based on deep misconceptions gets nowhere fast. If you really care you're going to have to go pick up some basics from not-an-HN-comment.
What constitutes a single work is basically what a person on the street would answer is a single thing. What constitutes a collective work is basically what a person on the street would call a collective work, after they answer the first question. (That is, if you start here they might say an album is one work, but if you get them to agree that a song is one thing once they probably won't say that.) What constitutes copying is basically what a person on the street would agree is copying. That certainly isn't good enough advice to go off of if you're going to try to build a business off of it or something, and edge cases abound, but the core concepts aren't anywhere near as screwed up as you might think. The problem isn't conceptual with copyright, it is how the concepts are used and abused.
The list of songs on CD isn't copyrightable -- it's a fact, not a creative expression. Taking a 5 second sample is most likely to be considered fair use.
I don't think any of this is too far off from common sense.
To the point below assuming a mashup is made by licensing samples from other works (avoiding fair use issues for a second) the Mashup would be a copyrightable work. But the authors of the individual samples still retain their own copyright.