Linguistics is the scientific study of language, including the study of grammar, syntax, phonetics, and specific branches like sociolinguistics and psycholinguistics. To speak a language natively means having unconscious knowledge of what is grammatically right or wrong in that language, which children acquire by age 5 without formal education by learning language similarly to how they learn to walk. Grammar refers to both the innate mental rules speakers have for combining sounds and words into sentences and assigning meaning, as well as linguistic theories that describe this competence.