In the study of language, description or descriptive linguistics is the work of objectively analyzing and describing how language is actually used (or how it was used in the past) by a group of people in a speech community.
All academic research in linguistics is descriptive; like all other scientific disciplines, its aim is to describe the reality as it is, without the bias of preconceived ideas about how it ought to be. Modern descriptive linguistics is based on a structural approach to language, as exemplified in the work of Leonard Bloomfield and others.
Linguistic description is often contrasted with linguistic prescription, which is found especially in education and in publishing. Prescription seeks to define standard language forms and give advice on effective language use, and can be thought of as a presentation of the fruits of descriptive research in a learnable form, though it also draws on more subjective aspects of language aesthetics. Prescription and description are complementary, but have different priorities and sometimes are seen to be in conflict. Description is sometimes distinguished from "descriptivism", which is then defined as the belief that description is more significant or important to teach, study, and practice than prescription.
As English-linguist Larry Andrews describes it, descriptive grammar is the linguistic approach that studies what a language is like, as opposed to prescriptive, which declares what a language should be like. In other words, descriptive grammarians focus analysis on how all sorts of people in all sorts of environments, usually in more casual, everyday settings, communicate, while prescriptive grammarians focus on the grammatical rules and structures predetermined by linguistic registers and figures of power for those who are under the control of said authorities to use. An example Andrews uses in his book is fewer than vs less than. A descriptive grammarian would state that both statements are correct, as long as the receiver of the message can understand the meaning behind the statement. A prescriptive grammarian, on the other hand, would analyze the rules and conventions behind the statements made and determine which statement is correct according to those rules. Andrews also believes that although the majority of linguists would be descriptive grammarians, the majority of public school teachers tend to be prescriptive.
Accurate description of real speech is a difficult problem, and linguists have often been reduced to approximations. Almost all linguistic theory has its origin in practical problems of descriptive linguistics. Phonology (and its theoretical developments, such as the phoneme) deals with the function and interpretation of sound in language. Syntax has developed to describe the rules concerning how words relate to each other in order to form sentences. Lexicology collects "words" and their derivations and transformations: it has not given rise to much generalized theory.
An extreme "mentalist" viewpoint denies that the linguistic description of a language can be done by anyone but a competent speaker. Such speakers have internalized something called "linguistic competence", which gives them the ability to extrapolate correctly from their experience new but correct expressions, and to reject expressions which do not convey meaning in the way the speaker intends. For example, an expression could be ambiguous, possibly leading to several different interpretations by the listener. Depending on the speaker's intent, ambiguity can be desirable (as in jokes and other humor) or not.
A linguistic description is considered descriptively adequate if it achieves one or more of the following goals of descriptive linguistics: