Aspiration of plosives
We have already highlighted how certain phonemes may be produced with an accompanying short puff of air in certain contexts. In particular, we considered the production of the voiceless alveolar plosive /t/ in the words top and stop (see What is an Allophone?) In the word top we saw that the /t/ is aspirated, i.e. /tɒp/ → [tʰɒp]. In the word stop, however, we saw that there is typically no aspiration, i.e. /stɒp/ → [stɒp]. We can say, therefore, that the phoneme /t/ has at least two allophones: [t] and [tʰ].
Aspiration also affects the two other voiceless plosives: the alveolar /p/ and the velar /k/. In fact, they are affected in the same way as /t/ when they occur in the same environments.
For example, /p/ is unaspirated when it follows /s/ (e.g. spin /spɪn/ → [spɪn]) but aspirated in a word such as pin, where /pɪn/ → [pʰɪn]. The phoneme /p/, therefore, has at least two allophones: [p] and [pʰ].
Similarly, /k/ is also unaspirated following a /s/ consonant (e.g. skin /skɪn/ → [skɪn]) but aspirated in a word such as kin (/kɪn/ → [kʰɪn]). The phoneme /k/ must also, therefore, have at least two allophones: [k] and [kʰ].
We see, then, that each of the voiceless plosives /p/, /t/ and /k/ has at least two allophones: an aspirated allophone [pʰ], [tʰ] and [kʰ], and an unaspirated allophone [p], [t], and [k]. The unaspirated allophones only occur after /s/.
Only plosive sounds can be aspirated and so there are no examples of nasals, fricatives, affricates or approximants being aspirated. Note also that only voiceless plosives are aspirated, i.e. the voiced plosives /b/, /d/ and /g/ are not aspirated (Table 5).
Table 5. Aspirated allophones.