What I'm curious about is what guides all these various interpretations?
What gives one more validity than another?
What do I need to study to begin to draw my own conclusions about the implications of a particular performers approach to ornamentation? If I were to simply employ my ears and (admittedly) unrefined musical sensibilites, I would favor Gould's approach, which seems to err on the side of less ornamentation and, when it is employed, it's done so in a simple, straight-forward manner. But it doesn't do _me_ any good to simply copy Gould's approach, so I need to find some way to understand the underlying thinking, so that I can develop my own feelings and interpretation.
what do you think of C.P.E. Bach's essay?
This is a great question! Although I agree with xvimbi to a certain extent that “taste” is necessary (I would say “good taste” though), I am not convinced at all that it is sufficient, or even the most important factor. For a start, who is going to be the arbiter of taste? I tend to regard music like I regard chess. Certainly it is a beautiful, elegant and aesthetically pleasing game, but taste, is hardly the criterion by which one would judge a game, although certainly the best games will have this component in it as well.Here are some more thoughts on this matter:4. So when you hear someone embellishing music contrary to respected editions directions, this maybe either because the performer is actually ignorant of them and just decided to follow his own “taste”, or it maybe because the performer has gone deeply into the Baroque mind and has come up with something that may actually approach an authentic ornamentation practice (although we can never be sure of that). Usually a bona fide performer will be able to explain his choice of ornamentation in a cogent manner, while an ignorant performer may babble something about “how good it all sounds”.