A phoneme is an abstract unit in the sound system of a language whose identity can distinguish one word from another. In English, for example, replacing /p/ with /k/ changes pill into kill, demonstrating that these sounds represent different phonemes. A phoneme is not a particular physical sound: it groups pronunciations that function as the same unit within a language. Phonemes are a central subject of phonology, the branch of linguistics concerned with the organization and patterning of linguistic sounds. (pressbooks.nvcc.edu)
Phonemes, phones, and allophones
A phone is a speech sound considered in terms of its physical production or acoustic properties. Phonetics describes such properties, whereas phonemic analysis investigates how sounds function within a particular linguistic system. Different phones that realize the same phoneme are called allophones. The distinction therefore separates an abstract category from its concrete pronunciations. (pressbooks.nvcc.edu)
English /t/ illustrates this relationship. In many North American varieties, it may be pronounced as an aspirated stop [tʰ] in atomic but as a tap [ɾ] in atom. Although these realizations differ physically, their distribution and the relationship between the words support treating them as realizations of one phoneme. The set of allophones belonging to a phoneme need not be identical across varieties of the same language. (pressbooks.nvcc.edu)
Contrast and minimal pairs
The clearest evidence for a phonemic distinction is a minimal pair: two words with different meanings whose pronunciations differ in just one segment at the same position. English pill–kill, lip–lick, and spill–skill establish the contrast between /p/ and /k/ in several environments. Differences in spelling are irrelevant to this test; the comparison concerns pronunciation. (pressbooks.nvcc.edu)
A single genuine minimal pair provides evidence that two sounds contrast. Nevertheless, the absence of a minimal pair does not automatically establish that they belong to one phoneme. The vocabulary available for analysis may contain accidental gaps, so linguists also examine near-minimal pairs, wider distributional patterns, and phonetic relationships. Establishing an inventory consequently requires analysis rather than simply collecting every audibly different sound. (pressbooks.nvcc.edu)
Predictable variation
Allophones commonly occur in complementary distribution: each occurs in an environment where the other does not. English /p/, /t/, and /k/ normally have aspirated realizations at the beginning of a stressed syllable, as in par, tar, and car. After /s/ within the same syllable, as in spar, star, and scar, they are normally unaspirated. This predictable difference does not create a separate set of English phonemes. (opentextbooks.rug.nl)
Other variation is less strictly determined by neighboring sounds. Speakers may use different realizations in the same environment without changing the word’s identity, traditionally described as free variation. Such variation may accompany speaking style rather than a lexical contrast. Conversely, a difference that is allophonic in one language can distinguish phonemes in another; phonemic status is language-specific, not an inherent property of a sound. (pressbooks.pub)
Transcription and writing
Phonemes are conventionally written between slashes, such as /t/, while phones and allophones appear in square brackets, such as [tʰ]. Symbols from the International Phonetic Alphabet are commonly used. The notation indicates the level of analysis: /t/ names a category, whereas [tʰ] specifies an aspirated pronunciation. A phonemic transcription therefore leaves out predictable details that a more detailed phonetic transcription may record. (opentextbooks.rug.nl)
Phonemes must also be distinguished from graphemes, the units of a writing system. Orthography represents language through historically established spelling conventions, not necessarily through a one-to-one correspondence between letters and phonemes. Letter-to-sound research consequently treats the alignment between written strings and pronunciation strings as a problem requiring explicit analysis. A phoneme inventory cannot simply be read off from a language’s alphabet. (arxiv.org)
Inventories and language variation
A phonemic inventory lists the contrastive consonants and vowels recognized in a language or specified variety. Languages differ substantially in inventory size. Ian Maddieson’s survey in the World Atlas of Language Structures reports consonant inventories ranging from 6 to 122 among its 566 sampled languages, with 22 the most frequent inventory size. These figures concern consonants, not the total number of phonemes. (wals.info)
Counts depend partly on analytical decisions. A complex articulation may be interpreted as one segment or as a sequence, while sounds occurring chiefly in borrowed vocabulary may receive different treatment. A description should therefore identify its assumptions and the dialect being analyzed rather than imply that every speaker necessarily shares one inventory. Cross-language comparison in linguistic typology requires consistent criteria for what counts as a contrastive segment. (wals.info)
Phonemes within larger structures
An inventory alone does not describe a sound system. Phonotactics governs permissible combinations and positions of sounds. English meek, for example, contains [m], [i], and [k], but rearranging those same sounds does not necessarily produce an acceptable English word. Phonemes function within structured sequences rather than as freely interchangeable building blocks. (pressbooks.nvcc.edu)
Their realizations may also depend on syllable structure, stress, and neighboring segments. Phonological descriptions can express these dependencies through rules linking abstract categories to context-specific pronunciations. Such analysis helps explain how speakers produce and recognize the same lexical units despite systematic differences in their physical realization. It distinguishes knowledge of a language’s sound patterns from the ability merely to identify individual speech sounds. (opentextbooks.rug.nl)