Phonemic distinction

Phonemic contrast refers to a minimal phonetic difference, that is, small differences in speech sounds, that makes a difference in how the sound is perceived by listeners, and can therefore lead to different mental lexical entries for words. For example, whether a sound is voiced or unvoiced (consider /b/ and /p/ in English) matters for how a sound is perceived in many languages, such that changing this phonetic feature can yield a different word (consider pat and bat in English); see Phoneme. Other examples in English of a phonemic contrast would be the difference between leak and league; the minimal difference of voicing between [k] and [g] does lead to the two utterances being perceived as different words. On the other hand, an example that is not a phonemic contrast in English is the difference between [sit] and [siːt]. In this case the minimal difference of vowel length is not a contrast in English and so those two forms would be perceived as different pronunciations of the same word seat.

Different phonetic realizations of the same phoneme are called allophones. Specific allophonic variations, and the particular correspondences between allophones (realizations of speech sound) and phonemes (underlying perceptions of speech sound) can vary even within languages. For example, speakers of Quebec French often express voiceless alveolar stops (/t/) as an affricate. An affricate is a stop followed by a fricative and in this case sounds like the English 'ch' sound. While this is an allophone of a single phoneme to speakers of Quebec French, to speakers of Belgian French this is heard as a stop followed by a fricative, or in other words as two different phonemes. This was accomplished by asking Belgian French speakers to repeat an utterance containing this affricate backwards, which resulted in the production of two separate sounds. If these speakers understood the affricate as a single sound, an allophone meant to stand in for the standard pronunciation [t], and not as two consecutive sounds, they would have reproduced the affricate exactly as is when they repeated the utterance backwards.

It is important not to mistake allophones, which are different manifestations of the same phoneme in speech, with allomorphs, which are morphemes that may sound different in different contexts. An example of allomorphy would be the English plural marker /s/, which can manifest as [s], [z], and [əz] (cats [kæts], dogs [dɒgz]).

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