|Social and cultural subfields|
Historical linguistics (also called diachronic linguistics) is the study of language change. It has five main concerns:
- to describe and account for observed changes in particular languages
- to reconstruct the pre-history of languages and determine their relatedness, grouping them into language families (comparative linguistics)
- to develop general theories about how and why language changes
- to describe the history of speech communities
- to study the history of words, i.e. etymology.
History and development 
At first, historical linguistics was comparative linguistics. Scholars were concerned chiefly with establishing language families and reconstructing prehistoric proto-languages, using the comparative method and internal reconstruction. The focus was initially on the well-known Indo-European languages, many of which had long written histories; the scholars also studied the Uralic languages, another European language family for which less early written material exists. Since then, there has been significant comparative linguistic work expanding outside of European languages as well, such as on the Austronesian languages and various families of Native American languages, among many others. Comparative linguistics is now, however, only a part of a more broadly conceived discipline of historical linguistics. For the Indo-European languages, comparative study is now a highly specialised field. Most research is being carried out on the subsequent development of these languages, in particular, the development of the modern standard varieties.
Some scholars have undertaken studies attempting to establish super-families, linking, for example, Indo-European, Uralic, and other families into Nostratic. These attempts have not been accepted widely. The information necessary to establish relatedness becomes less available as the time depth is increased. The time-depth of linguistic methods is limited due to chance word resemblances and variations between language groups, but a limit of around 10,000 years is often assumed. The dating of the various proto-languages is also difficult; several methods are available for dating, but only approximate results can be obtained.
Evolution into other fields 
Initially, all modern linguistics was historical in orientation. Even the study of modern dialects involved looking at their origins. Ferdinand de Saussure's distinction between synchronic and diachronic linguistics is fundamental to the present day organization of the discipline. Primacy is accorded to synchronic linguistics, and diachronic linguistics is defined as the study of successive synchronic stages. Saussure's clear demarcation, however, is now seen to be idealised.
In practice, a purely synchronic linguistics is not possible for any period before the invention of the gramophone, as written records always lag behind speech in reflecting linguistic developments. Written records are difficult to date accurately before the development of the modern title page. Also, the work of sociolinguists on linguistic variation has shown synchronic states are not uniform: the speech habits of older and younger speakers differ in ways that point to language change. Synchronic variation is linguistic change in progress.
The biological origin of language is in principle a concern of historical linguistics, but most linguists regard it as too remote to be reliably established by standard techniques of historical linguistics, such as the comparative method. Less-standard techniques, such as mass lexical comparison, are used by some linguists to overcome the limitations of the comparative method, but most linguists regard them as unreliable.
The findings of historical linguistics are often used as a basis for hypotheses about the groupings and movements of peoples, particularly in the prehistoric period. In practice, however, it is often unclear how to integrate the linguistic evidence with the archaeological or genetic evidence. For example, there are numerous theories concerning the homeland and early movements of the Proto-Indo-Europeans, each with its own interpretation of the archaeological record.
Sub-fields of study 
Comparative linguistics 
Comparative linguistics (originally comparative philology) is a branch of historical linguistics that is concerned with comparing languages in order to establish their historical relatedness. Languages may be related by convergence through borrowing or by genetic descent, thus languages can change and are also able to cross-relate.
Genetic relatedness implies a common origin or proto-language. Comparative linguistics has the goal of constructing language families, reconstructing proto-languages, and specifying the changes that have resulted in the documented languages. To maintain a clear distinction between attested language and reconstructed forms, comparative linguists prefix an asterisk to any form that is not found in surviving texts.
Etymology is the study of the history of words — when they entered a language, from what source, and how their form and meaning have changed over time. A word may enter a language as a loanword (i.e., as a word from one language adopted by speakers of another language), through derivational morphology by combining pre-existing elements in the language, by a hybrid of these two processes called phono-semantic matching, or in several other minor ways.
In languages with a long and detailed history, etymology makes use of philology, the study of how words change from culture to culture over time. Etymologists also apply the methods of comparative linguistics to reconstruct information about languages that are too old for any direct information (such as writing) to be known. By analyzing related languages with a technique known as the comparative method, linguists can make inferences, about their shared parent language and its vocabulary. In this way, word roots that can be traced all the way back to the origin of, for instance, the Indo-European language family have been found. Although originating in the philological tradition, much current etymological research is done in language families for which little or no early documentation is available, such as Uralic and Austronesian.
Dialectology is the scientific study of linguistic dialect, the varieties of a language that are characteristic of particular groups, based primarily on geographic distribution and their associated features. This is in contrast to variations based on social factors, which are studied in sociolinguistics, or variations based on time, which are studied in historical linguistics. Dialectology treats such topics as divergence of two local dialects from a common ancestor and synchronic variation.
Dialectologists are concerned with grammatical features that correspond to regional areas. Thus, they are usually dealing with populations living in specific locales for generations without moving, but also with immigrant groups bringing their languages to new settlements.
Phonology is a sub-field of linguistics which studies the sound system of a specific language or set of languages. Whereas phonetics is about the physical production and perception of the sounds of speech, phonology describes the way sounds function within a given language or across languages.
An important part of phonology is studying which sounds are distinctive units within a language. For example, the "p" in "pin" is aspirated while the "p" in "spin" is not. In English these two sounds are used in complementary distribution and are therefore not used to differentiate words and so are considered allophones of the same phoneme. In some other languages, for example Thai and Quechua, this same difference of aspiration or non-aspiration does differentiate words and these two sounds phones are therefore considered phonemes.
The principles of phonological theory have also been applied to the analysis of sign languages, although the phonological units do not consist of sounds. The principles of phonological analysis can be applied independently of modality because they are designed to serve as general analytical tools, not language-specific ones.
Morphology is the study of the formal means of expression in a language; in the context of historical linguistics, how the formal means of expression change over time; for instance, languages with complex inflectional systems tend to be subject to a simplification process. This field studies the internal structure of words as a formal means of expression.
Words as units in the lexicon are the subject matter of lexicology. While words are generally accepted as being (with clitics) the smallest units of syntax, it is clear that, in most (if not all) languages, words can be related to other words by rules. The rules understood by the speaker reflect specific patterns (or regularities) in the way words are formed from smaller units and how those smaller units interact in speech. In this way, morphology is the branch of linguistics that studies patterns of word-formation within and across languages, and attempts to formulate rules that model the knowledge of the speakers of those languages, in the context of historical linguistics, how the means of expression change over time. See grammaticalisation.
Syntax is the study of the principles and rules for constructing sentences in natural languages. The term syntax is used to refer directly to the rules and principles that govern the sentence structure of any individual language, as in "the syntax of Modern Irish". Modern researchers in syntax attempt to describe languages in terms of such rules. Many professionals in this discipline attempt to find general rules that apply to all natural languages in the context of historical linguistics, how characteristics of sentence structure in related languages changed over time. See grammaticalisation.
Conservative, innovative, archaic 
The terms "conservative" and "innovative" are often used in historical linguistics to characterize the extent of change occurring in a particular language or dialect as compared with related varieties. In particular, a conservative variety has changed relatively less than an innovative variety. These descriptive terms carry no value judgment. A particularly conservative variety that preserves features that have long since vanished elsewhere is sometimes said to be "archaic".
See also 
- Comparative linguistics
- Comparative method
- Comparative word lists:
- Genetic linguistics
- Germanic philology
- Indo-European studies
- Language change
- Language families and languages
- List of language histories
- List of languages by first written accounts
- Mass lexical comparison
- Ural–Altaic languages
Citations and notes 
- A formal language is a set of words, i.e. finite strings of letters or symbols. The inventory from which these letters are taken is the alphabet through which the language is defined. A formal language is often defined by means of a formal grammar, but it does not describe their semantics (i.e., what they mean)
||This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. (April 2007)|
- Bernd Kortmann: English Linguistics: Essentials, Anglistik-Amerikanistik, Cornlesen, p. 37-49
Recommended readings 
- Karl Brugmann, Berthold Delbrück, Grundriss der vergleichenden Grammatik der indogermanischen Sprachen (1886–1916).
- Theodora Bynon, Historical Linguistics (Cambridge University Press, 1977) ISBN 0-521-29188-7
- Henry M. Hoenigswald, Language change and linguistic reconstruction (Chicago: Univ. of Chicago Press 1960).
- Richard D. Janda and Brian D. Joseph (Eds), The Handbook of Historical Linguistics (Blackwell, 2004) ISBN 1-4051-2747-3
- Roger Lass, Historical linguistics and language change. (Cambridge University Press, 1997) ISBN 0-521-45924-9
- Winfred P. Lehmann, Historical Linguistics: An Introduction (Second Edition) (Holt, 1973) ISBN 0-03-078370-4
- April McMahon, Understanding Language Change (Cambridge University Press, 1994) ISBN 0-521-44665-1
- James Milroy, Linguistic Variation and Change (Blackwell, 1992) ISBN 0-631-14367-X
- M.L. Samuels, Linguistic Evolution (Cambridge University Press, 1972) ISBN 0-521-29188-7
- R.L. Trask,(ed.) Dictionary of Historical and Comparative Linguistics (Fitzroy Dearborn, 2001) ISBN 1-57958-218-4
- August Schleicher: Compendium der vergleichenden Grammatik der indogermanischen Sprachen. (Kurzer Abriss der indogermanischen Ursprache, des Altindischen, Altiranischen, Altgriechischen, Altitalischen, Altkeltischen, Altslawischen, Litauischen und Altdeutschen.) (2 vols.) Weimar, H. Boehlau (1861/62); reprinted by Minerva GmbH, Wissenschaftlicher Verlag, ISBN 3-8102-1071-4
- Zuckermann, Ghil'ad (2003). Language Contact and Lexical Enrichment in Israeli Hebrew. Palgrave Macmillan. ISBN 1-4039-1723-X.