One's competence is defined by the grammar, or set of language rules, that is represented mentally and manifested based on his or her own understanding of acceptable usage in a given linguistic idiom. Therefore, grammatical competence defines an innate knowledge of rules rather than knowledge of items or relations. According to Chomsky, it is regarded to be innate because one does not have to be trained to develop it and will still be able to apply it in an infinite number of unheard examples.[4]
The core components of the grammar are included in the speaker's linguistic competence and these components corresponds to five of the major subfields of linguistics:
Phonetics: The physical production and perception of the inventory of sounds used in producing language.
Phonology: The mental organization of physical sounds and the patterns formed by the way sounds are combined in a language, and the restrictions on permissible sound combinations.
E.g.: slip vs *psil and *sbill
Morphology: The identification, analysis and description of units of meaning in a language. One will know the inflectional and derivational morphology present in the language, such as the affixes of words.
E.g.: re-cuddle can be derived but not *re-rich
Syntax: The structure and formation of sentences. One can distinguish between grammatical sentences and ungrammatical sentences.
E.g.: My hair needs washing is acceptable but not *My hair needs wash
Semantics: Understanding the meaning of sentences. This is also how a user of the language is able to understand and interpret the non-literal meaning in a given utterance. They are three distinctions drawn here:
(i) Meaningful and non-meaningful sentences
E.g.: The accident was seen by thousands is meaningful but not *The accident was looked by thousands
(ii) Same structure but different meanings
E.g.: The cow was found by the stream versus The cow was found by the farmer
(iii) Different structures and still be able to relate the meanings
E.g.: The police examined the bullet.
The bullet was examined by the police.