So as I understand, Moore's Open Question Argument can be formulated like this:
I. If x is the same thing as y, then the question "I know it's x, but is it y?" would be meaningless
II. The question "I know it's x, but is it good?" where x is some natural property is meaningful.
Therefore, good cannot be defined in terms of natural properties.
The thing I'm having trouble with is the second premise. If I said "I know he's a bachelor, but is he unmarried?" the question would seem to only reflect that I don't know what the heck the word "bachelor" means. But isn't he assuming that that isn't the case with the question "I know it's x, but is it good?"
In other words, couldn't it just be the case that, since it's possible that simply no one is properly informed on what "good" means, "x is good" could be a question of identity? Isn't he assuming it isn't, just because the two terms "feel" different?
For example. Let's say that no one on Earth knew what "bachelor" meant. So if someone asked "I know he's a bachelor, but is he unmarried?" that would seem like a genuinely meaningful question. In the same way, couldn't it be the case that "x is good" where x is some natural property, for example "'pleasurable' is 'good'", is genuinely a question of identity, it's just no one knows the true nature of good, so it feels like a meaningful question to ask?
Sorry if this isn't too lucid of a question.