Allophony

Allophony is a concept in phonology describing how a single phoneme can have multiple phonetic realizations, called allophones. These realizations occur in predictable environments and do not distinguish meaning in the language. In contrast, phonemes are the abstract units that can contrast to differentiate words. Allophony accounts for how underlying sound inventories are realized in actual speech.

Allophony can be categorized by distribution. In complementary distribution, different allophones never appear in the same environment, and their use is conditioned by context. A classic example is English voiceless stops: the /p/ of "pin" is aspirated [pʰ], while the /p/ in "spin" is typically unaspirated [p], with the two realizations never occurring in the same phonetic environment. In free variation, allophones can alternate without changing word identity, with the choice often depending on speaker or regional variation.

Other well-known cases include the alveolar tap [ɾ], which is an allophone of /t/ and /d/ in American English when it occurs between vowels and the second vowel is unstressed. The surface sound changes, but the underlying phoneme remains the same, so no new word is formed. Allophony is language-specific and is analyzed within phonology to explain how phonetic detail emerges from abstract phoneme representations, without requiring additional phonemes.