Phoneme

A phoneme is a group of similar speech sounds that native speakers of a language perceive as a single, basic unit of sound—the smallest one that can change a word’s meaning. Every language has phonemes (or their equivalent in sign languages, which use space and gesture), and all spoken languages include both consonant and vowel phonemes. The study of phonemes falls under phonology, a subfield of linguistics, the scientific study of language, writing, speech, and related topics.

When written, phonemes are traditionally shown as a character between two forward slashes, like /ɒ/, which represents the set of sounds in the middle of the English word *pot*. The actual pronunciation of this phoneme varies by accent—for instance, [ɔ] in many British and Australian accents, [ɑ] in many U.S. and Irish accents, and [a] in Great Lakes U.S. accents—but it still counts as one phoneme because it contrasts with /ʊ/ in *put* or /ɪ/ in *pit*.

The words *cell* and *set* differ only in their final consonant: /sɛl/ versus /sɛt/ in the International Phonetic Alphabet (IPA), a writing system for representing phonemes. Because /l/ and /t/ alone distinguish these words, they are phonemes of English—specifically consonant phonemes, along with /s/, while /ɛ/ is a vowel phoneme. English spelling often does not match its phonemes closely. For example, *knot*, *nut*, and *gnat* share the consonant phonemes /n/ and /t/, differing only in their vowel phonemes: /ɒ/, /ʌ/, and /æ/. Another example is /pʊʃt/, which transcribes the four phonemes /p/, /ʊ/, /ʃ/, and /t/ that make up the pronunciation of *pushed*.

Phonemes are perceived differently by speakers of different languages. For instance, [n] and [ŋ] are separate phonemes in English, distinguishing *sin* from *sing* (/sɪn/ versus /sɪŋ/), but they form a single phoneme in Spanish, where [pan] and [paŋ] are heard as just regional variants of the same word (*pan*, meaning "bread"). These spoken variations of a single phoneme are called allophones. Conversely, [y] and [u] are usually heard as variations of one phoneme in English, but they are separate phonemes in French, which distinguishes *rue* ("street," /ʁy/) from *roue* ("wheel," /ʁu/).

Linguists use slashes in the IPA for phonemic transcription and square brackets for phonetic transcription, which includes allophones and precise pronunciation details. So, the pronunciations of *tap* versus *tab*, or *pat* versus *bat*, are written between slashes (/p/, /b/, etc.), while nuances like the aspirated [pʰ] in *pit* versus the unaspirated [p] in *spit* are written between brackets.

There are many theories about what phonemes are and how to analyze them in a language. Generally, a phoneme is seen as an abstraction of a set of sound variations that native speakers perceive as a single basic unit. While phonemes are abstract, underlying representations of sound segments in words, their phonetic realizations—each phoneme with its allophones—are the surface forms actually spoken and heard. Allophones have technically different articulations in specific words or environments, but these differences do not create meaningful distinctions; at least one articulation could be used in all such words and still be recognized by speakers. For example, in American English, the sound spelled *t* is often pronounced as a glottal stop [ʔ] in *cat*, an alveolar flap [ɾ] in *dating*, an alveolar plosive [t] in *stick*, and an aspirated alveolar plosive [tʰ] in *tie*, yet speakers perceive all these as allophones of the single phoneme /t/.

For computer typing, systems like X-SAMPA represent IPA symbols with ASCII characters. Descriptions of particular languages may use different conventional symbols for their phonemes. For languages with phonemic writing systems, ordinary letters may denote phonemes, but this is often imperfect because pronunciations shift over time, making spelling outdated or less representative of actual sounds.