Exactly. Terry Tao calls this having a "post-rigorous" understanding (https://terrytao.wordpress.com/career-advice/there’s-more-to-mathematics-than-rigour-and-p

Exactly. Terry Tao calls this having a "post-rigorous" understanding (https://terrytao.wordpress.com/career-advice/there’s-more-to-mathematics-than-rigour-and-proofs/ https://terrytao.wordpress.com/career-advice/there’s-more-to...). We can't think the formal rules are sufficient. (And in the case of adjectives, it seems explicit knowledge of the formal rules aren't even necessary for fluency.)