Phonology is a branch of linguistics concerned with the systematic organization of sounds in languages. It has traditionally focused largely on study of the systems of phonemes in particular languages, but it may also cover any linguistic analysis either at a level beneath the word (including syllable, onset and rhyme, articulatory gestures, articulatory features, mora, etc.) or at all levels of language where sound is considered to be structured for conveying linguistic meaning. Phonology also includes the study of equivalent organizational systems in sign languages.
The word phonology (as in the phonology of English) can also refer to the phonological system (sound system) of a given language. This is one of the fundamental systems which a language is considered to comprise, like its syntax and its vocabulary.
Phonology is often distinguished from phonetics. While phonetics concerns the physical production, acoustic transmission and perception of the sounds of speech, phonology describes the way sounds function within a given language or across languages to encode meaning. For many linguists, phonetics belongs to descriptive linguistics, and phonology to theoretical linguistics, although establishing the phonological system of a language is necessarily an application of theoretical principles to analysis of phonetic evidence. Note that this distinction was not always made, particularly before the development of the modern concept of phoneme in the mid 20th century. Some subfields of modern phonology have a crossover with phonetics in descriptive disciplines such as psycholinguistics and speech perception, resulting in specific areas like articulatory phonology or laboratory phonology.
Derivation and definitions 
Definitions of the term vary. Nikolai Trubetzkoy in Grundzüge der Phonologie (1939) defines phonology as "the study of sound pertaining to the system of language", as opposed to phonetics, which is "the study of sound pertaining to the act of speech" (the distinction between language and speech being basically Saussure's distinction between langue and parole). More recently, Lass (1998) writes that phonology refers broadly to the subdiscipline of linguistics concerned with the sounds of language, while in more narrow terms, "phonology proper is concerned with the function, behaviour and organization of sounds as linguistic items". According to Clark et al. (2007) it means the systematic use of sound to encode meaning in any spoken human language, or the field of linguistics studying this use.
Development of phonology 
The history of phonology may be traced back to the Ashtadhyayi, the Sanskrit grammar composed by Pāṇini in the 4th century BC. In particular the Shiva Sutras, an auxiliary text to the Ashtadhyayi, introduces what can be considered a list of the phonemes of the Sanskrit language, with a notational system for them that is used throughout the main text, which deals with matters of morphology, syntax and semantics.
The Polish scholar Jan Baudouin de Courtenay (together with his former student Mikołaj Kruszewski) introduced the concept of the phoneme in 1876, and his work, though often unacknowledged, is considered to be the starting point of modern phonology. He also worked on the theory of phonetic alternations (what is now called allophony and morphophonology), and had a significant influence on the work of Ferdinand de Saussure.
An influential school of phonology in the interwar period was the Prague school. One of its leading members was Prince Nikolai Trubetzkoy, whose Grundzüge der Phonologie (Principles of Phonology), published posthumously in 1939, is among the most important works in the field from this period. Directly influenced by Baudouin de Courtenay, Trubetzkoy is considered the founder of morphophonology, although this concept had also been recognized by de Courtenay. Trubetzkoy also developed the concept of the archiphoneme. Another important figure in the Prague school was Roman Jakobson, who was one of the most prominent linguists of the 20th century.
In 1968 Noam Chomsky and Morris Halle published The Sound Pattern of English (SPE), the basis for generative phonology. In this view, phonological representations are sequences of segments made up of distinctive features. These features were an expansion of earlier work by Roman Jakobson, Gunnar Fant, and Morris Halle. The features describe aspects of articulation and perception, are from a universally fixed set, and have the binary values + or −. There are at least two levels of representation: underlying representation and surface phonetic representation. Ordered phonological rules govern how underlying representation is transformed into the actual pronunciation (the so-called surface form). An important consequence of the influence SPE had on phonological theory was the downplaying of the syllable and the emphasis on segments. Furthermore, the generativists folded morphophonology into phonology, which both solved and created problems.
Natural phonology was a theory based on the publications of its proponent David Stampe in 1969 and (more explicitly) in 1979. In this view, phonology is based on a set of universal phonological processes which interact with one another; which ones are active and which are suppressed are language-specific. Rather than acting on segments, phonological processes act on distinctive features within prosodic groups. Prosodic groups can be as small as a part of a syllable or as large as an entire utterance. Phonological processes are unordered with respect to each other and apply simultaneously (though the output of one process may be the input to another). The second-most prominent natural phonologist is Stampe's wife, Patricia Donegan; there are many Natural Phonologists in Europe, though also a few others in the U.S., such as Geoffrey Nathan. The principles of natural phonology were extended to morphology by Wolfgang U. Dressler, who founded natural morphology.
In 1976 John Goldsmith introduced autosegmental phonology. Phonological phenomena are no longer seen as operating on one linear sequence of segments, called phonemes or feature combinations, but rather as involving some parallel sequences of features which reside on multiple tiers. Autosegmental phonology later evolved into feature geometry, which became the standard theory of representation for the theories of the organization of phonology as different as lexical phonology and optimality theory.
Government phonology, which originated in the early 1980s as an attempt to unify theoretical notions of syntactic and phonological structures, is based on the notion that all languages necessarily follow a small set of principles and vary according to their selection of certain binary parameters. That is, all languages' phonological structures are essentially the same, but there is restricted variation that accounts for differences in surface realizations. Principles are held to be inviolable, though parameters may sometimes come into conflict. Prominent figures include Jonathan Kaye, Jean Lowenstamm, Jean-Roger Vergnaud, Monik Charette, John Harris, and many others.
In a course at the LSA summer institute in 1991, Alan Prince and Paul Smolensky developed optimality theory—an overall architecture for phonology according to which languages choose a pronunciation of a word that best satisfies a list of constraints which is ordered by importance: a lower-ranked constraint can be violated when the violation is necessary in order to obey a higher-ranked constraint. The approach was soon extended to morphology by John McCarthy and Alan Prince, and has become a dominant trend in phonology. Though this usually goes unacknowledged, optimality theory was strongly influenced by natural phonology; both view phonology in terms of constraints on speakers and their production, though these constraints are formalized in very different ways. The appeal to phonetic grounding of constraints in various approaches has been criticized by proponents of 'substance-free phonology'.
Broadly speaking, government phonology (or its descendant, strict-CV phonology) has a greater following in the United Kingdom, whereas optimality theory is predominant in North America.
Analysis of phonemes 
An important part of traditional, pre-generative, schools of phonology is studying which sounds can be grouped into distinctive units within a language; these units are known as phonemes. For example, in English, the "p" sound in pot is aspirated (pronounced [pʰ]), while that in spot is not aspirated (pronounced [p]). However, English speakers intuitively treat both sounds as variations (allophones) of the same phonological category, that is, of the phoneme /p/. (Traditionally, it would be argued that if an aspirated [pʰ] were interchanged with the unaspirated [p] in spot, native speakers of English would still hear the same words; that is, the two sounds are perceived as "the same" /p/.) In some other languages, however, these two sounds are perceived as different, and they are consequently assigned to different phonemes in those languages. For example, in Thai, Hindi, and Quechua, there are minimal pairs of words for which aspiration is the only contrasting feature (two words with different meanings that are identical except that one has an aspirated sound where the other has an unaspirated one).
Part of the phonological study of a language therefore involves looking at data (phonetic transcriptions of the speech of native speakers) and trying to deduce what the underlying phonemes are and what the sound inventory of the language is. The presence or absence of minimal pairs, as mentioned above, is a frequently used criterion for deciding whether two sounds should be assigned to the same phoneme. However other considerations often need to be taken into account as well.
The particular sounds which are phonemic in a language can change over time. At one time, [f] and [v] were allophones in English, but these later changed into separate phonemes. This is one of the main factors of historical change of languages as described in historical linguistics.
The findings and insights of speech perception and articulation research complicates the traditional and somewhat intuitive idea of interchangeable allophones being perceived as the same phoneme. First, interchanged allophones of the same phoneme can result in unrecognizable words. Second, actual speech, even at a word level, is highly co-articulated, so it is problematic to expect to be able to splice words into simple segments without affecting speech perception.
Different linguists therefore take different approaches to the problem of assigning sounds to phonemes. For example, they differ in the extent to which they require allophones to be phonetically similar. There are also differing ideas as to whether this grouping of sounds is purely a tool for linguistic analysis, or reflects an actual process in the way the human brain processes a language.
Since the early 1960s, theoretical linguists have moved away from the traditional concept of a phoneme, preferring to consider basic units at a more abstract level, as a component of morphemes; these units can be called morphophonemes, and analysis using this approach is called morphophonology.
Other topics in phonology 
In addition to the minimal units that can serve the purpose of differentiating meaning (the phonemes), phonology studies how sounds alternate, i.e. replace one another in different forms of the same morpheme (allomorphs), as well as, for example, syllable structure, stress, accent, and intonation.
Phonology also includes topics such as phonotactics (the phonological constraints on what sounds can appear in what positions in a given language) and phonological alternation (how the pronunciation of a sound changes through the application of phonological rules, sometimes in a given order which can be feeding or bleeding,) as well as prosody, the study of suprasegmentals and topics such as stress and intonation.
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. The same principles have been applied to the analysis of sign languages (see Phonemes in sign languages), even though the sub-lexical units are not instantiated as speech sounds.
See also 
- Absolute neutralisation
- English phonology
- List of phonologists (also Category: Phonologists)
- Phonological development
- Phonological hierarchy
- Prosody (linguistics)
- Second language phonology
- Lass, Roger (1998. Digitized 2000). Phonology: An Introduction to Basic Concepts. Cambridge, UK; New York; Melbourne, Australia: Cambridge University Press. p. 1. ISBN 0-521-23728-9. Retrieved 8 January 2011 Paperback ISBN 0-521-28183-0
- Carr, Philip (2003). English Phonetics and Phonology: An Introduction. Massachusetts, USA; Oxford, UK; Victoria, Australia; Berlin, Germany: Blackwell Publishing. ISBN 0-631-19775-3. Retrieved 8 January 2011 Paperback ISBN 0-631-19776-1
- Trubetzkoy N., Grundzüge der Phonologie (published 1939), translated by C. Baltaxe as Principles of Phonology, University of California Press, 1969
- Clark, John; Yallop, Colin; Fletcher, Janet (2007). An Introduction to Phonetics and Phonology (3rd ed.). Massachusetts, USA; Oxford, UK; Victoria, Australia: Blackwell Publishing. ISBN 978-1-4051-3083-7. Retrieved 8 January 2011 Alternative ISBN 1-4051-3083-0
- Hale, Mark; Reiss, Charles (2008). The Phonological Enterprise. Oxford, UK: Oxford University Press. ISBN 0-19-953397-0.
- Goldsmith 1995:1.
- Anderson, John M.; and Ewen, Colin J. (1987). Principles of dependency phonology. Cambridge: Cambridge University Press.
- Bloch, Bernard (1941). "Phonemic overlapping". American Speech 16 (4): 278–284. doi:10.2307/486567. JSTOR 486567.
- Bloomfield, Leonard. (1933). Language. New York: H. Holt and Company. (Revised version of Bloomfield's 1914 An introduction to the study of language).
- Brentari, Diane (1998). A prosodic model of sign language phonology. Cambridge, MA: MIT Press.
- Chomsky, Noam. (1964). Current issues in linguistic theory. In J. A. Fodor and J. J. Katz (Eds.), The structure of language: Readings in the philosophy language (pp. 91–112). Englewood Cliffs, NJ: Prentice-Hall.
- Chomsky, Noam; and Halle, Morris. (1968). The sound pattern of English. New York: Harper & Row.
- Clements, George N. (1985). "The geometry of phonological features". Phonology Yearbook 2: 225–252. doi:10.1017/S0952675700000440.
- Clements, George N.; and Samuel J. Keyser. (1983). CV phonology: A generative theory of the syllable. Linguistic inquiry monographs (No. 9). Cambridge, MA: MIT Press. ISBN 0-262-53047-3 (pbk); ISBN 0-262-03098-5 (hbk).
- de Lacy, Paul, ed. (2007). The Cambridge Handbook of Phonology. Cambridge University Press. ISBN 0-521-84879-2 (hbk). Retrieved 8 January 2011
- Donegan, Patricia. (1985). On the Natural Phonology of Vowels. New York: Garland. ISBN 0-8240-5424-5.
- Firth, J. R. (1948). "Sounds and prosodies". Transactions of the Philological Society 47 (1): 127–152. doi:10.1111/j.1467-968X.1948.tb00556.x.
- Gilbers, Dicky; de Hoop, Helen (1998). "Conflicting constraints: An introduction to optimality theory". Lingua 104: 1–12. doi:10.1016/S0024-3841(97)00021-1.
- Goldsmith, John A. (1979). The aims of autosegmental phonology. In D. A. Dinnsen (Ed.), Current approaches to phonological theory (pp. 202–222). Bloomington: Indiana University Press.
- Goldsmith, John A. (1989). Autosegmental and metrical phonology: A new synthesis. Oxford: Basil Blackwell.
- Goldsmith, John A (1995). "Phonological Theory". In John A. Goldsmith. The Handbook of Phonological Theory. Blackwell Handbooks in Linguistics. Blackwell Publishers. ISBN 1-4051-5768-2.
- Gussenhoven, Carlos & Jacobs, Haike. "Understanding Phonology", Hodder & Arnold, 1998. 2nd edition 2005.
- Hale, Mark; Reiss, Charles (2008). The Phonological Enterprise. Oxford, UK: Oxford University Press. ISBN 0-19-953397-0.
- Halle, Morris (1954). "The strategy of phonemics". Word 10: 197–209.
- Halle, Morris. (1959). The sound pattern of Russian. The Hague: Mouton.
- Harris, Zellig. (1951). Methods in structural linguistics. Chicago: Chicago University Press.
- Hockett, Charles F. (1955). A manual of phonology. Indiana University publications in anthropology and linguistics, memoirs II. Baltimore: Waverley Press.
- Hooper, Joan B. (1976). An introduction to natural generative phonology. New York: Academic Press.
- Jakobson, Roman (1949). "On the identification of phonemic entities". Travaux du Cercle Linguistique de Copenhague 5: 205–213. doi:10.1080/01050206.1949.10416304.
- Jakobson, Roman; Fant, Gunnar; and Halle, Morris. (1952). Preliminaries to speech analysis: The distinctive features and their correlates. Cambridge, MA: MIT Press.
- Kaisse, Ellen M.; and Shaw, Patricia A. (1985). On the theory of lexical phonology. In E. Colin and J. Anderson (Eds.), Phonology Yearbook 2 (pp. 1–30).
- Kenstowicz, Michael. Phonology in generative grammar. Oxford: Basil Blackwell.
- Ladefoged, Peter. (1982). A course in phonetics (2nd ed.). London: Harcourt Brace Jovanovich.
- Martinet, André. (1949). Phonology as functional phonetics. Oxford: Blackwell.
- Martinet, André. (1955). Économie des changements phonétiques: Traité de phonologie diachronique. Berne: A. Francke S.A.
- Napoli, Donna Jo (1996. Linguistics: An Introduction. New York: Oxford University Press.
- Pike, Kenneth. (1947). Phonemics: A technique for reducing languages to writing. Ann Arbor: University of Michigan Press.
- Sandler, Wendy and Lillo-Martin, Diane. 2006. Sign language and linguistic universals. Cambridge: Cambridge University Press
- Sapir, Edward (1925). "Sound patterns in language". Language 1 (2): 37–51. doi:10.2307/409004. JSTOR 409004.
- Sapir, Edward (1933). "La réalité psychologique des phonémes". Journal de Psychologie Normale et Pathologique 30: 247–265.
- de Saussure, Ferdinand. (1916). Cours de linguistique générale. Paris: Payot.
- Stampe, David. (1979). A dissertation on natural phonology. New York: Garland.
- Swadesh, Morris (1934). "The phonemic principle". Language 10 (2): 117–129. doi:10.2307/409603. JSTOR 409603.
- Trager, George L.; Bloch, Bernard (1941). "The syllabic phonemes of English". Language 17 (3): 223–246. doi:10.2307/409203. JSTOR 409203.
- Trubetzkoy, Nikolai. (1939). Grundzüge der Phonologie. Travaux du Cercle Linguistique de Prague 7.
- Twaddell, William F. (1935). On defining the phoneme. Language monograph no. 16. Language.