Phonology is a subfield of grammar (see also linguistics). Whereas phonetics is about the nature of sounds (or phones) per se, phonology describes the way sounds function within a given language. For example, /p/ and /b/ in English are distinctive units of sound, (i.e., phonemes.) We can tell this from minimal pairs such as "pin" and "bin", which mean different things, but differ only in one sound.
Note that the principles of phonological theory have also been applied to the analysis of signed languages, with gestures and their relationships as the object of study.
Phonemes and spelling
In some languages the phonemes are directly linked to spelling, i.e., a phoneme is represented by a graphical symbol or a combination of them, a letter or a letter combination. However in English different phonemes can be spelled the same way ("good" and "food" have different vowel sounds), so one should use the International Phonetic Alphabet (IPA) to denote phonemes. To indicate that one means names instead of phones the phoneme or sequence of phonemes is enclosed by two slashes (or solidi) " / / " (without the quotes or pluralization; see above examples).
Doing a phoneme inventory
Part of the phonological study of a language 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.
Even though a language may make distinctions between a small number of phonemes, speakers actually produce many more phonetic sounds. Thus, a phoneme in a particular language can be pronounced in many ways.
Looking for minimal pairs forms part of the research in studying the phoneme inventory of a language. However with this method it is often not possible to detect all phonemes so other approaches are used as well. A minimal pair is a pair of words, both from the same language, that differ by only a single phoneme, and that are recognized by speakers as being two different words.
When there is a minimal pair, then those two sounds constitute separate phonemes, otherwise they are called allophones of the same underlying phoneme. For instance, voiceless stops (/p/, /t/, /k/) can be aspirated. In English, word initial voiceless stops are aspirated, whereas non word-initial voiceless stops are not aspirated (This can be seen by putting your fingers right in front of your lips and notice the difference in breathiness as you say 'pin' and 'spin'). There is no English word 'pin' that starts with an unaspirated p, therefore in English, aspirated [pʰ] (the [ʰ] means aspirated) and unaspirated [p] are allophones of an underlying phoneme /p/.
Another example... in English, the liquids /l/ and /ɹ / are two separate phonemes (minimal pair 'life', 'rife'); however, in Korean these two liquids are allophones of the same phoneme, and the general rule is that [ɾ] comes before a vowel, and [l] doesn't (e.g. Seoul, Korea). A native speaker of Korean will tell you that the [l] in Seoul and the [ɾ] in Korea are in fact the same letter. What happens is that a native Korean speaker's brain uses the underlying phoneme /l/, and depending on the phonetic context (before a vowel or not) this phoneme gets expressed as either the [ɾ] sound or the [l] sound. Another Korean speaker will hear both sounds as the underlying phoneme and think of them as the same sound. This is one reason why most people have an accent when they attempt to speak a language that they did not grow up hearing; their brains sort the sounds they hear in terms of the phonemes of their own native language.
Noam Chomsky and Morris Halle presented in The Sound Pattern of English a view of phonology where a phonological representation (surface syntactic form) is a structure whose phonetic part is a sequence of units which have characteristic features. Although there are no phonemes in generative phonology, these units are often loosely referred to as phonemes, nonetheless. The features describe aspects of articulation and perception, are from a universally fixed set and have the binary values + or -. Phonological rules govern how this phonological representation (also called underlying representation) is transformed into the actual pronunciation (also called surface form.)
Change of a phoneme inventory over time
The particular sounds that a language decides to make distinctions between can change over time as new children learn the language. At one point, [f] and [v] were allophones in English, and these changed later into separate phonemes. This is one of the main factors of historical change of languages as described in historical linguistics (another being fast change resulting from influence by another language, e.g. French influence on English after the Norman Conquest).
Other languages features studied in phonology
Stress and tone are also part of phonology. In some languages, stress is non-phonological, e.g. in Finnish or in all ancient Germanic languages, e.g. Old Norse, Old English and Old High German as well as some modern Germanic languages such as Icelandic. However, in most modern-day Germanic languages such as German or English, stress is indeed phonologically distinctive, although there are only few minimal pairs, e.g. /'august/ 'August (the name)' versus /au'gust/ 'August (the month)' in German, or /kQn'v3:s/(RP) /kən'vɝs/(GenAm) 'converse (to hold a conversation)' and /'kQnv3:s/(RP) /'kɑnvɚs/(GenAm) 'converse (the opposite of something)' in English.
Development of the field
In 1976 John Goldsmith introduced autosegmental phonology. The phonological phenomena are no longer seen as one linear sequence of segments called phonemes or feature combinations but rather as some parallel sequences of features which reside on multiple tiers.
In the late 1980s, 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 became a dominant trend in phonology of the 1990s and beyond.
- On-line phonology course (of English)
- Another on-line phonology course dealing with English using large amounts of Macromedia_Flash interaction.