It’s easily characterized more realistically in the real world. If you
know how the English language works, it doesn’t mean that you’d be good
at it — you have to know the words you could use to convey the message
you want to express. So sentence formation (subject verb agreement,
appropriate tense, etc.) is not the crux of learning English (or any
spoken language for that matter) but rather the actual use (practice)
and semantics of the language — as well as an expanded vocabulary of
the terms available to the user.