In a language or dialect, a phoneme (from the Greek: φώνημα, phōnēma, "a sound uttered") is the smallest segmental unit of sound employed to form meaningful contrasts between utterances.[1]
Thus 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 of a phoneme is the /k/ sound in the words kit and skill. (In transcription, phonemes are placed between slashes, as here.) Although most native English speakers don't notice this, in most English dialects, the /k/ sounds in these two words are actually pronounced differently: they are different speech sounds, or phones (which, in transcription, are placed in square brackets). In our example, the /k/ in kit is aspirated, [kʰ], while the /k/ in skill is unaspirated. The reason why these different sounds are nonetheless considered to belong to the same phoneme in English is that if an English-speaker used one instead of the other, the meaning of the word would not change: using [kʰ] in skill might sound odd, but the word would still be recognized. By contrast, some other phonemes could be substituted (creating a minimal pair) which would cause a change in meaning: producing words like still (substituting /t/), spill (substituting /p/) and swill (substituting /w/). These other sounds (/t/, /p/ and /w/) are, in English, different phonemes.
In some languages, however, [kʰ] and [k] are different phonemes, and are perceived as such by the speakers of those languages. For example, in Icelandic, /kʰ/ is the first sound of kátur meaning 'cheerful', while /k/ is the first sound of gátur meaning 'riddles'. The fact that these two different words have different meanings which can be readily identified by speakers of Icelandic tells us that Icelandic speakers perceive the sounds as different phonemes.
Diagram of basic procedure to determine whether two sounds are phonemesPhones that belong to the same phoneme, such as [t] and [tʰ] for English /t/, are called allophones. A common test to determine whether two phones are allophones of the same phoneme or separate phonemes relies on finding minimal pairs: words that differ by only the phone in question. For example, the words tip and dip illustrate that in English [t] and [d] are separate phonemes, /t/ and /d/, in English: the two words have different meanings that are readily recognizable, meaning that English speakers can readily distinguish between the two sounds. In other languages, though, including Korean; there are no such pairs available. The lack of minimal pairs distinguishing /t/ and /d/ in Korean indicates that in this language they are allophones of a single phoneme /t/. (/tʰata/ is pronounced [tʰada], for example. That is, when they hear this one word, Korean speakers perceive the same sound in both the beginning and middle of the word, whereas an English speaker would perceive different sounds in these two locations.)
Some linguists (such as Roman Jakobson, Morris Halle, and Noam Chomsky) consider phonemes to be further decomposable into features, such features being the true minimal constituents of language. Features overlap each other in time, as do suprasegmental phonemes in oral language and many phonemes in sign languages. Features could be designated as acoustic (Jakobson) or articulatory (Halle & Chomsky) in nature
