A phoneme () is a set of similar speech sounds that are perceptually regarded by the speakers of a language as a single basic sound—the smallest possible phonetic unit—that helps distinguish one word from another. All languages contain phonemes (or the spatial–gestural equivalent in sign languages), and all spoken languages include both consonant and vowel phonemes. Phonemes are studied under phonology, a branch of linguistics, a discipline encompassing the scientific study of language, writing, speech, and related matters. Phonemes are traditionally represented, when written, as a glyph (a character) enclosed within two forward-sloping slashes /. For example, /ɒ/ indicates the phoneme, or set of sounds, used in the middle of the English word pot. The exact phonetic reality of this phoneme varies by accent, with the pronunciation [ɔ] in many British and Australian accents, [ɑ] in many US and Irish accents, [a] in Great Lakes accents of the US, etc. Still, /ɒ/ counts as one phoneme because it contrasts with, say, the /ʊ/ of put or /ɪ/ of pit.
Overview
The words cell and set have the same sequence of sounds except for the final consonant: thus, /sɛl/ versus /sɛt/ in the International Phonetic Alphabet (IPA), which is a writing system that can be used to represent phonemes. Since /l/ and /t/ alone distinguish the spoken words cell and set, /l/ and /t/ are examples of phonemes of the English language. Specifically they are consonant phonemes, along with the /s/, while /ɛ/ is a vowel phoneme. English spelling does not always closely align with its phonemes. For example, the English words knot, nut, and gnat all share the consonant phonemes /n/ and /t/, differing only by their vowel phonemes: /ɒ/, /ʌ/, and /æ/, respectively. Another example of phonemic transcription is /pʊʃt/: the notation for a sequence of four phonemes—/p/, /ʊ/, /ʃ/, and /t/—that constitutes the pronunciation of the word pushed. Phonemes, or word-distinguishing sounds (or sets of sounds), are perceived differently by users of one language versus another. For example, [n] and [ŋ] are separate phonemes in English as they distinguish words like sin from words like sing (/sɪn/ versus /sɪŋ/), but they constitute a single phoneme in other languages, such as Spanish, in which [pan] and [paŋ] for instance are interpreted by Spanish speakers as merely regional or dialect-specific pronunciations of the same word (pan: the Spanish word for "bread"). Such spoken variations of a single phoneme are known by linguists as allophones. On the other hand, [y] and [u] are usually heard as variations on one phoneme in English, though they are completely separate phonemes in other languages, like French, which distinguishes words such as rue, "street" /ʁy/ from roue, "wheel" /ʁu/. Linguists use slashes in the IPA to transcribe phonemes, and square brackets to transcribe more precise pronunciation details, including allophones; they describe this distinction as phonemic versus phonetic. Thus, the pronunciations of tap versus tab, or pat versus bat, can be represented phonemically and are written between slashes (/p/, /b/, etc.), while nuances of exactly how speakers pronounce /p/ are phonetic and written between brackets, such as [p] for the p in spit versus [pʰ] for the p in pit, which in English is an aspirated allophone of /p/ (i.e., pronounced with an extra burst of air).
Conceptual basis; theory of the definition of phonemes There are many views as to exactly what phonemes are and how a given language should be analyzed in phonemic terms. Generally, a phoneme is regarded as an abstraction of a set (or equivalence class) of spoken sound variations that are nevertheless perceived as a single basic unit of sound by the ordinary native speakers of a given language. While phonemes are considered abstracted, underlying representations for sound segments within words, the corresponding phonetic realizations of those phonemes—each phoneme with its various allophones—constitute the surface form that is actually uttered and heard. Allophones each have technically different articulations inside particular words or particular environments within words, yet these differences do not create any meaningful distinctions. Alternatively, at least one of those articulations could be feasibly used in all such words with these words still being recognized as such by users of the language. An example in American English is that the sound spelled with the symbol t is usually articulated with a glottal stop [ʔ] (or a similar glottalized sound) in the word cat, an alveolar flap [ɾ] in dating, an alveolar plosive [t] in stick, and an aspirated alveolar plosive [tʰ] in tie; however, American English speakers perceive or "hear" all of these sounds (usually with no conscious effort) as merely being allophones of a single phoneme: the one traditionally represented in the IPA as /t/. For computer-typing purposes, systems such as X-SAMPA exist to represent IPA symbols using only ASCII characters. However, descriptions of particular languages may use different conventional symbols to represent the phonemes of those languages. For languages whose writing systems employ the phonemic principle, ordinary letters may be used to denote phonemes, although this approach is often imperfect, as pronunciations naturally shift in a language over time, rendering previous spelling systems outdated or no longer closely representative of the sounds of the language (see further the section headed § Correspondence between letters and phonemes, below).
Assignment of speech sounds to phonemes
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