Prescriptive grammars, on the other hand, assume the existence of better authorities than the usage and judgment of native speakers. People who write prescriptive grammars adduce better language users (educated speakers, high-class speakers, great writers), better languages (usually Latin) and better information systems (mathematics or predicate calculus) as authorities for preferring one usage over another. Prescriptive rules exist only to express a preference for one structure or usage or linguistic item over another. A prescriptive grammar will not contain rules that tell you to put articles before nouns, rather than after, because no native speakers of English put articles after nouns. Prescriptive rules are reserved for places where speakers have choices and they exist to limit those choices.