Allophone

In phonetics, an allophone is one of several similar phones that belong to the same phoneme. A phone is a sound that has a definite shape as a sound wave, while a phoneme is a basic group of sounds that can distinguish words (i.e. changing one phoneme in a word can produce another word); speakers of a particular language perceive a phoneme as a single distinctive sound in that language. Thus an allophone is a phone considered as a member of one phoneme.

We may distinguish complementary allophones, which are distributed regularly within the idiolect of the same speaker according to phonetic environment, from free variants, which are a matter of personal habit or regional accent.

In the case of complementary allophones, each allophone is used in a specific phonetic context and many times there is some sort of phonological process. Not all phonemes have significantly different allophones, but there are always minor differences in articulation from one piece of speech to the next.

Examples in English
For example, as in pin and  as in spin are allophones for the phoneme  in the English language because they occur in complementary distribution. English speakers generally treat these as the same sound, but they are different; the first is aspirated and the second is unaspirated (plain). Plain also occurs as the p in cap, or the second p in paper. In contexts where plain p appears in English (e.g. spin, cap, paper), speakers may hear it as b since the p in these contexts lacks the burst of air found with the p in pin. Besides, there are many different allophones in English, like lack of plosion, nasal plosion, partial devoicing of sonorants, complete devoicing of sonorants, partial devoicing of obstruents, lengthening and shortening vowels, dentalisation and retruction.


 * Aspiration – strong explosion of breath. In English a voiceless plosive that is p, t or k is aspirated whenever it stands as the only consonant at the beginning of the stressed syllable.


 * Lack of plosion – In English a plosive (p, t, k, b, d, g) has no plosion when it is followed by another plosive or an affricate inside words or across word boundary.


 * Nasal plosion – In English a plosive (p, t, k, b, d, g) has nasal plosion when it’s followed by nasal, inside a word or across word boundary.


 * Partial devoicing of sonorants – In English a non vocalic sonorant that is not a vowel (j, w, l, r, m, n, ŋ) is partially devoiced when it follows a voiceless sound within the same way inside a word.


 * Complete devoicing of sonorants – In English a non vocalic sonorant is completely devoiced in the position of aspiration, when they follow a voiceless plosives (p, t, k) standing as the first consonant at the beginning of the stressed syllable.


 * Partial devoicing of obstruents – in English language a voiced obstruent is partially devoiced next to a pause or next to a voiceless sound, inside a word or across it’s boundary.


 * Dentalisation – in English t, d, n, l are becoming dental before voiced and voiceless English ‘th’ sound.


 * Retruction – in English t, d, n, l are retructed before r.

Certain Chinese languages treat these two phones differently, for example in Mandarin, is always written b in pinyin; thus, they are not allophones.

English-speaking people may become aware of the difference between two allophones of the phoneme t when they consider the pronunciations of the following phrases:


 * Night rate: IPA
 * Nitrate: IPA

"Elsewhere" condition
When there are two allophones for one phoneme in a given language, linguists use the "elsewhere condition" to determine which is the original allophone and which is the variation. For example, to determine when oral and nasalized vowels occur in English, the pattern is noted that all vowels are oral, except when the vowel comes before a nasal within the same syllable. Therefore, according to the "elsewhere condition", nasalized vowels are allophones of their oral counterparts.