Acquiring the grammar competence of the speakers’ native language, requires the learning of forms instead of learning other cognitive skills.

Communicative competence is the knowledge included in grammatical competence plus the ability to use that knowledge to accomplish a wide range of communicative jobs, and they are part of the language linguistic study. 

Linguistics think that language structure and grammar competence must be included in the language use and, the mental aspect should be added. 

Language structure competence and the different systems of communication are recognized as a different language if they cannot be understood. 

The combination of grammatical competence with the knowledge of how to use grammatical sentences (and other pieces of linguistics structure) appropriately to the purpose and context at hand, by speakers, make communication more effective.