In linguistics, grammar is the system of rules that governs how a natural language is structured and used, as evidenced by its speakers or writers. Grammar rules may concern the use of clauses, phrases, and words. The term may also refer to the study of such rules, a subject that includes phonology, morphology, and syntax, together with phonetics, semantics, and pragmatics. There are in effect two different ways to study grammar: traditional grammar and theoretical grammar.