Descriptive linguistics is the work of analyzing and describing how language is spoken (or how it was spoken in the past) by a group of people in a speech community.
The priorities of descriptive linguistics are essentially incongruous with those of prescriptive grammar, which is concerned not with describing how a language is actually spoken, but rather with pronouncing, in the form of normative statements or rules, how language users ought to properly speak or write a language. Accurate description of real speech is a difficult problem, and linguists have often been reduced to grossly inaccurate 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 how native speakers pronounce their languages. Syntax has developed to describe what happens when phonetics has reduced spoken language to a normalized control level. Lexicography 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 a speaker has internalized something called "linguistic competence", which gives them the ability to extrapolate correctly from their experience new but correct expressions, and to reject unacceptable expressions.
There are tens of thousands of linguistic descriptions of thousands of languages that were prepared by people without adequate linguistic training. With a few honorable exceptions, all linguistic descriptions done before ca. 1900 are amateur productions.
A linguistic description is considered descriptively adequate if it achieves one or more of the following goals of descriptive linguistics:
- A description of the phonology of the language in question.
- A description of the morphology of words belonging to that language.
- A description of the syntax of well-formed sentences of that language.
- A description of lexical derivations.
- A documentation of the vocabulary, including at least one thousand entries.
- A reproduction of a few genuine texts.
There are some bonus topics that might also be included, like an analysis of discourse and historical reconstructions.
Currently the most controversial topics are usually morphology and syntax. English has a very meager morphology and an over-emphasized syntax, but in the study of other languages, morphology has revived as an active field of study.
The purpose of linguistic theory, so far as a practical linguist is concerned, is to make descriptions of morphology and syntax comprehensible. It is easy to see that the same data can often be described in different ways. For a while there was an active desire to find some measure which would allow some one description to be called the best. Today that goal seems to have been given up as chimerical.