Grammar refers to the set of rules governing the composition of language. It includes morphology, syntax, phonology, and other linguistic fields. While linguists study these structural rules, non-linguists may use the term more broadly to refer to any aspect of language they object to. The term can also describe the rules governing a group of speakers. Adjectives, verbs, and prepositions are important parts of language that add details and establish relationships to complete meaning. The earliest systematic grammars were developed in Iron Age India.