[mparke]

I really like what you've said here. However I'd like to suggest that you've narrowed Mastery quite a bit, The way I see it, proficiency can come with with the ability to guide an alien through the world you understand, but mastery might exist as your very own specific understanding (which when measured against another's mastery might not even be in the same range of comparison ). I might try even argue your point differently, maybe your proficiency represents the ability for you to compare to another person's proficiency in a common subject, which allows you to achieve conciseness when discussing the subject. And your mastery is merely a completely individual experience. Just thinking out loud here. Again well said.