A phoneme is a basic unit of sound in a language, and thus, a sound that can distinguish one word from another in a particular language. A phoneme can have slightly different variants, or allophones, in different contexts, because each sound is influenced by the sounds before and after it. But native speakers would judge the allophones of a phoneme to be all the same sound.
Phonemes and phonological transriptions are represented with slash marks, like /p/, while allophones in more detailed phonetic transcriptions are written with square brackets, like [pʰ]. Angled brackets here indicate word spellings, e.g, <pat>.
- The /n/ in English is an alveolar nasal sound. The tongue tip is on the alveolar ridge, and air escapes through the nose, giving it a resonant quality. Before a dental sound like /θ/ in 'tenth,' the /n/ takes on a more dental pronunciation, but most native English speakers do not notice this difference.
- The /æ/ in 'camper' is generally slightly nasalized, but native English speakers would not notice this, unless it is a particularly strong nasalization, such as the heavy nasalization in some southern US dialects. In some Texas dialects, for example, 'camper' is heard clearly as [kæ̃mpɜɹ].
- The /t/ before an unstressed vowel in American English is pronounced not as a soft [t], but as a light alveolar flap, /ɾ/, as in 'butter.' In other contexts, such as before an /n/ of a following unstressed syllable, as in 'button,' it can be heard as a nasally released [tⁿ] or as a glottal stop [ʔ], which is not a regular phoneme of English.
- The /p/ phoneme in English is a bilabial stop (plosive) consonant, and is often aspirated, or pronounced with a puff of air, the allophone [pʰ], before stressed vowels in stressed syllables, as in 'pie.' The unaspirated or soft [p] allophone of /p/ occurs before unstressed syllables, and thus the <p> in words like 'rápper' is the soft [p]. The soft [p] also occurs after <s> in the <sp> combination in a syllable onset, and thus, the <sp> in 'spit' is [sp]. Another allophone is the unreleased [p̚], in which the lips block the airflow and the air is not released at the end; thus, the <p> in 'stop' and 'stapler' sounds like [p̚]. However, most native English speakers do not notice these differences, and consider them all to be one sound.
We can determine if two sounds are phonemes by testing them with minimal pairs. We can try these sounds for English:
- [p̚at], [pat], [pʰat]
and would find that they all sound like the same word, <pot>. We could also could try these sounds for English:
- [tæp̚], [tæp], [tæpʰ]
We would find they all sound like the same word, <tap>. Thus, these are not separate phonemes, but allophones of one /p/ sound. We can contrast /p/ with other sounds to show that /p/ is a phoneme that is distinct from other labial sounds, the /b/, /f/ and /v/, e.g.:
- /p/ ≠ /b/: pat, bat
- /p/ ≠ /f/: pat, fat
- /p/ ≠ /v/: pat, vat
Native speakers do not usually hear distinctive phonemes, because their minds interpret various allophones of a phoneme as one sound. This is because phonemes are more abstract, psychological categories, that allow us to interpret words despite slight variations in pronunciation depending on the phonetic context of a sound, or slight differences in how various speakers pronounce a phoneme.