Broadly conceived, linguistics is the study of human language and a linguist is someone who engages in this study. Linguistic inquiry is pursued by a wide variety of specialists, who may not all be in harmonious agreement; as Russ Rymer[?] flamboyantly puts it
Linguists often divide the study of language into a number of separate areas, to be studied more or less independently. The following divisions are currently popular:
Note that not all linguists agree that all these divisions are meaningful. Most cognitive linguists, for example, would probably find the categories "semantics" and "pragmatics" to be arbitrary, and nearly all linguists would agree that the divisions overlap considerably. The term grammar usually covers phonology, morphology and syntax.
Linguists can be broadly divided into those that study language at a particular point in time (usually the present) and those that study how language changes through time, sometimes over centuries. In somewhat dated terminology, this is the contrast between diachronic and synchronic linguistics. To some extent, linguists from each camp find the other camp to be less interesting, and ultimately less insightful.
Nonetheless, language is complex enough to support many perspectives. Surely it is valuable to know both the exact ways in which a particular grammatical construction is used by present-day English speakers and the historical process by which that construction entered the English language.
Some insight into language can come only from a historical perspective. Understanding how a language can influence or even transform into others requires a historical perspective, for example.
In American universities, the non-historic perspective seems to have the upper hand. Many introductory linguistics classes, for example, have almost no historic component whatsoever. Brown University has no department of linguistics, but rather a single "Department of Cognitive Science and Linguistics"; cognitive science tends to be somewhat non-historic in character, and so does the linguistics work of the department. This shift in focus to a non-historic perspective has started with Saussure and became predominant with Noam Chomsky.
People aside from professional linguists also seem to have different feelings of the importance of the historical portion of linguistic analysis. People may disagree, for example, on how important historical usage and etymology are for "truly understanding" a word. Fans of the Oxford English Dictionary tend to view outdated and aging language as more important in understanding a word's meaning than fans of Webster's Dictionary.
Linguists also differ in how broad a group of language users they study. Some analyze a given speaker's language or language development in great detail. Some study language pertaining to a whole speech community, such as the language of all those who speak Black English Vernacular. Others try to find linguistic universals that apply, at some abstract level, to all users of human language everywhere. This latter project has been most famously been advocated by Noam Chomsky, and it interests many people in psycholinguistics and cognitive science. It is thought that universals in human language may reveal important insight into universals about the human mind.
Probably most work currently done under the name "linguistics" is purely descriptive, the linguists seeking to clarify the nature of language without passing value judgments or trying to chart future language directions. Nonetheless, there are many professionals and amateurs who also prescribe rules of language, perhaps holding a particular standard out for all to follow.
The two groups may describe the same phenomenon in different language. What to one group is "incorrect usage" is, to the other group, "idiosyncratic usage", or perhaps simply the usage of a particular (and usually less powerful) subgroup.
People engaged in descriptive and prescriptive efforts often have serious disagreements about how and why language should be studied.
A number of contemporary linguists have the intuition that speech is more important to study than writing. Perhaps this is because speech appears to be a human universal, whereas many cultures without writing have been discovered. The fact that people learn to speak and process oral language easier and earlier than writing also factors in. A number of cognitive scientists argue that the brain has an innate "language module", knowledge of which is thought to come more from studying speech than writing.
Writing is by no means no longer studied, however. New ways to study it continue to be created. For example, at the intersection of corpus linguistics and computational linguistics, computer models are often trained on tens of thousands of examples of written language from, say, the Wall Street Journal. Similar databases of spoken language are simply unavailable.
phonetics, phonology, syntax, semantics, pragmatics, etymology, lexicology, lexicography, theoretical linguistics, historical-comparative linguistics and descriptive linguistics, etymology, computational linguistics, corpus linguistics, semiotics.
historical linguistics, orthography, writing systems, comparative linguistics[?], cryptanalysis, decipherment, sociolinguistics, psycholinguistics, language acquisition, evolutionary linguistics, anthropological linguistics[?], stratificational linguistics, cognitive science, neurolinguistics, and in computer science there is natural language understanding, speech recognition, speaker recognition[?] (authentication), speech synthesis, and more generally, speech processing
Noam Chomsky's formal model of language, transformational-generative grammar, developed under the influence of his teacher Zellig Harris[?], who was in turn strongly influenced by Leonard Bloomfield, has been the dominant one from the 1960s. Since then Steven Pinker has gone on to clarify and simplify Chomsky's original ideas with much broader significance to the study of language in general.
Other important linguists and schools include Michael Halliday, whose systemic functional grammar is pursued widely in the U.K., Canada, Australia, China, and Japan; Dell Hymes, who developed a pragmatic approach called The Ethnography of Speaking; George Lakoff, Len Talmy[?], and Ronald Langacker[?], who were pioneers in cognitive linguistics; Charles Fillmore[?] and Adele Goldberg, who are associated with construction grammar[?]; and linguists developing several varieties of what they call functional grammar, including Talmy Givon[?] and Robert Van Valin, Jr. Also, Ferdinand de Saussure, founder of structural linguistics.
"Linguistics" and "linguist" may not always be meant to apply as broadly as above. In some contexts, the best definitions may be "what is studied in a typical university's department of linguistics", and "one who is a professor in such a department." Linguistics in this narrow sense usually does not refer to learning to speak foreign languages (except insofar as this helps to craft formal models of language.) It does not include literary analysis. Only sometimes does it include study of things such as metaphor. It probably does not apply to those engaged in such proscriptive efforts as found in Strunk and White's The Elements of Style; "linguists" usually seek to study what people do, not what they should do. One could probably argue for a long while about who is and who is not a "linguist".