That's a bizarre choice of example. The question of whether Pluto is a planet is entirely a definitional one; the IAU could make it one by fiat if they chose. There's no particular reason for it not to be one, except that the IAU felt the increasing number of tranNeptunian objects made the current definition awkward.
"[E]ntirely a definitional" question does not mean "arbitrary and trivial" - some definitions are just wrong. EY mentions the classic example in Where to Draw the Boundary?:
...Once upon a time it was thought that the word "fish" included dolphins. Now you could play the oh-so-clever arguer, and say, "The list: {Salmon, guppies, sharks, dolphins, trout} is just a list - you can't say that a list is wrong. I can prove in set theory that this list exists. So my definition of fish, which is simply this extensional list, ca
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Part 2