Metaphysics Backwards

One of the things one learns in Music Theory is the idea of musical forms (Sonata form etc.). Such things are useful, of course, and even understandable, but one thing always bothers me when I am in a philosophic mood. How is it possible to say whether a piece of music has the qualities necessary to give it the nature of a sonata when it has a few exceptions to the rules that define the form? For example, if a piece has everything required by the form except that the second theme in the first section is in the same key as the first theme in the first section, is it still a sonata. Common sense would seem to say yes, as would a music teacher. But what about the metaphysician? Similarly, if an animal had everything that an elephant had except that it was orange or could jump or...you get the picture, would it still be an elephant? A biologist would say no, common sense would say yes...what would the metaphysician say?

Quite honestly, I don't know what the metaphysicians of the world say on this fine point. (I know what Chesterton said: that exceptions should be treated as exceptions and then ignored.) But I suggest this: that the analytical methods of music theory could possibly be applied in an analogical way to metaphysics to give us a way of handling the natures of exceptions. Any thoughts?