Because languages naturally adapt to their situations of use and also reflect the social identities of their speakers, linguistic variation is inevitable and natural. In some nations, language academies have been established to settle such matters, as with the French Academy, formed nearly four hundred years ago, but to date English speakers have repudiated suggestions of a regulating body for their language. Instead, entrepreneurs like Noah Webster have earned their living by writing dictionaries and grammars, usually with a mix of description and prescription. Increasingly, though, scholarly grammars and dictionaries are exclusively descriptive. Prescriptivists follow the tradition of the classical grammars of Sanskrit, Greek, and Latin, which aimed to preserve earlier forms of those languages so that readers in subsequent generations could understand sacred texts and historical documents.
Modern grammarians aim to describe rather than prescribe linguistic forms and their uses.
Dictionary makers also strive for descriptive accuracy in reporting which words are in use and which senses they carry. In order to write accurate descriptions, grammarians must identify which expressions are actually in use. Investigating 'slow' and 'slowly', they would find that both forms function as adverbs, and they might uncover situational or social-group correlates for them. Descriptivists would point out that English has made no distinction between the adjective and adverb forms of 'fast' for over five hundred years, but prescriptivists are not concerned about that. Descriptivists might also note that different social groups favor one expression or the other in conversation, while only the latter appears in published writing.