When acquiring knowledge of a language code (its grammatical system), either the mother tongue or foreign (or second), a major role is played by an intuitive, non-materialized, subjective grammatical rule acquired, as well as a cognitive, explicitly formulated rule learned. A non-native speaker needs complex instructions about the target language, both about the formal aspect and the speech (functional, semantic) dimension.
A native speaker also needs an instruction, he may find difficult to describe in detail on a satisfactory level the more advanced chapters of Czech grammar.