Grammatical ability refers to knowing how grammar is used in communication.
What are the grammatical competence?
1. The mastery of the linguistic code. It is the ability to recognize lexical, morphological, syntactical, and phonological features of a language and to use these features effectively to interpret, encode, and decode words and sentences.
Why do we need to possess grammatical competence?
For different discourse situations we apply different sentence patterns, vocabulary layers and structures. Consequently, the due level of grammar competence helps us to realize the rule of 5Cs, which make our speech clear, correct, concise, coherent and cohesive.