My most "frequently asked question" of the exam period has been, what is the rule for improper appropriation? I don't intend to provide an exhaustive answer here, so don't rely on this brief note to the exclusion of your casebook, lecture notes, and mind maps. But hopefully, I can restate things a bit more clearly.
First, don't forget that this test is one of two prongs. The plaintiff must also show that defendant copied, through the "access" + "probative similarity" test (or through striking similarity).
As I said in class, i think that the casebook presents a very muddled analysis on pages 616-643. In particular, the "By Way of Overview" pages, section 8.03[C][1] on 616-621 are unnecessarily complex.
Most courts engage in two steps, as listed on 616. First, did defendant take "protected expression?" Second, did plaintiff show that the intended audience will recognize "substantial similarities" between the two works? Confusingly, some courts don't even engage in these two steps cleanly, and they sometimes smoosh the two together. (See, for example, the Laureyssens court's formulation of the test on 637.) It is often useful to think of this as two steps, however.
With the first step, there is some variety in how it is applied. But courts tend to be more objective in this step. They tend to use analytic dissection to strip away unprotectable things (facts/ideas/things in the public domain) and then analyze the copyrightability with what is left.
With the second step, there is also some variety. But courts tend to be more subjective, looking at "total concept and feel," and viewing things from the point of view of the ordinary observer (and don't forget our conversation about the different ways to analyze the ordinary observer.)
I guess the point I'm trying to make is don't try too hard to look for unifying tests always to apply for this test. Get a handle on the cases we discussed in class for this section, and maybe make a little chart about the mode of analysis used in each case. Take note of the type of work at issue in each case, bearing in mind my hunch that the test used has a lot to do with the type of work.
Let me know if this still doesn't make sense.