Copying the description of the argument from the Stanford Encyclopedia of Philosophy, with just one bolded replacement of a definition irrelevant to the formal validity of the argument:
Say that an entity possesses “maximal excellence” if and only if it is a flying pig. Say, further, that an entity possesses “maximal greatness” if and only if it possesses maximal excellence in every possible world—that is, if and only if it is necessarily existent and necessarily maximally excellent. Then consider the following argument:
There is a possible world in which there is an entity which possesses maximal greatness.
(Hence) There is an entity which possesses maximal greatness.
Perhaps. It’s not clear to me that this is irrelevant to the formal validity of the argument, since “is a typical pig in all respects, and flies” seems to be a contradiction, and replacing a term in an argument with a contradiction isn’t necessarily truth-preserving. But perhaps it is, I don’t know… common sense would reject it, but we’re clearly not operating in the realms of common sense here.
Copying the description of the argument from the Stanford Encyclopedia of Philosophy, with just one bolded replacement of a definition irrelevant to the formal validity of the argument:
This argument proves that at least one pig can fly. I understand “pigs fly” to mean something more like “for all X, if X is a typical pig, X can fly.”
You are right. Perhaps the argument could be modified by replacing “is a flying pig” by “is a typical pig in all respects, and flies”?
Perhaps. It’s not clear to me that this is irrelevant to the formal validity of the argument, since “is a typical pig in all respects, and flies” seems to be a contradiction, and replacing a term in an argument with a contradiction isn’t necessarily truth-preserving. But perhaps it is, I don’t know… common sense would reject it, but we’re clearly not operating in the realms of common sense here.