Phoneme

A phoneme (/ˈfoʊniːm/) is any set of similar speech sounds that are perceptually regarded by the speakers of a language as a single basic sound—a 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 the discipline of linguistics (a field encompassing language, writing, speech and related matters).

Phonemes are often represented, when written, as a glyph (a character) enclosed within two forward-sloping slashes /. So, for example, /k/ represents the phoneme or sound used in the beginning of the English language word cat (as opposed to, say, the /b/ of bat).

The English words cell and set have the exact same sequence of sounds, except for being different in the sound of their final consonant: thus, /sɛl/ versus /sɛt/ in the International Phonetic Alphabet (IPA) (a writing system that can be used to represent phonemes). Since /l/ and /t/ alone distinguish certain words from others, they are each examples of phonemes of the English language. Specifically they are consonant phonemes, along with /s/, while /ɛ/ is a vowel phoneme. The spelling of English does not strictly conform to its phonemes, so that the words knot, nut, and gnat, regardless of spelling, all share the consonant phonemes /n/ and /t/, differing only by their internal vowel phonemes: /ɒ/, /ʌ/, and /æ/, respectively. Similarly, /pʊʃt/ is the notation for a sequence of four phonemes — /p/, /ʊ/, /ʃ/ and /t/ — that when spoken together in order constitute the vocalised word pushed.

Sounds that are perceived as phonemes vary by language and by dialect. So, for example, [n] ^ⓘ and [ŋ] ^ⓘ are separate phonemes in English since they distinguish words like sin from words like sing (/sɪn/ versus /sɪŋ/); yet they comprise a single phoneme in some other languages, such as Spanish, in which [pan] and [paŋ] for instance are merely interpreted by Spanish speakers as regional or dialect-specific ways of pronouncing the same word (pan: the Spanish word for "bread"). Such spoken variations of a single phoneme are known by linguists as allophones. Linguists use slashes in the IPA to transcribe phonemes but square brackets to transcribe more precise pronunciation details, including allophones; they describe this basic distinction as phonemic versus phonetic. Thus, the pronunciation patterns of tap versus tab, or pat versus bat, can be represented phonemically and are written between slashes (including /p/, /b/, etc.), while nuances of exactly how a speaker pronounces /p/ are phonetic and written between brackets, like [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).

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).

A phoneme is a sound or a group of different sounds perceived to have the same function by speakers of the language or dialect in question. An example is the English phoneme /k/, which occurs in words such as cat, kit, scat, skit. Although most native speakers do not notice this, in most English dialects, the "c/k" sounds in these words are not identical: in kit^ⓘ [kʰɪt], the sound is aspirated, but in skill^ⓘ [skɪl], it is unaspirated. The words, therefore, contain different speech sounds, or phones, transcribed [kʰ] for the aspirated form and [k] for the unaspirated one. These different sounds are nonetheless considered to belong to the same phoneme, because if a speaker used one instead of the other, the meaning of the word would not change: using the aspirated form [kʰ] in skill might sound odd, but the word would still be recognized. By contrast, some other sounds would cause a change in meaning if substituted: for example, substitution of the sound [t] would produce the different word still, and that sound must therefore be considered to represent a different phoneme (the phoneme /t/).

The above shows that in English, [k] and [kʰ] are allophones of a single phoneme /k/. In some languages, however, [kʰ] and [k] are perceived by native speakers as significantly different sounds, and substituting one for the other can change the meaning of a word. In those languages, therefore, the two sounds represent different phonemes. For example, in Icelandic, [kʰ] is the first sound of kátur, meaning "cheerful", but [k] is the first sound of gátur, meaning "riddles". Icelandic, therefore, has two separate phonemes /kʰ/ and /k/.