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Here under are the rules for voiceless plosives consonants: p, t, k and examples for illustration.
(a) initial position: in initial position / p t k / are strong sounds, they have special features that they cause the following sounds to lose some of their voicing which it would otherwise have, apart from that, when they stand in initial position of a stressed syllable, they are aspirated
For examples:
important / ɪmphɔːtənt /
intelligent / ɪnthelɪdʒɜːnt /
income /ɪnkhʌm/
pool / phuːl /
tone/thʌn /
port / phɔːt/ v.v..
(b) Weak aspiration (middle position): voiceless plosives will be weak when they end a stressed syllable. Old theory stated that when voiceless plosives occur between vowels, the aspiration may be less noticeable or even absent, but it will never do any harm to keep this aspiration in this position too, for examples:
upper /`ʌpə /
outer / `aʊtə /
supper / `sʌpə /
happy /`hæpɪ /
writer/`raɪtə /
latter/`lætə/
water/`wɔːtə/
liking/`laɪkɪŋ/
licking /`lɪkɪŋ /
weaker /`wiːkə/.
(c) In final position: voiceless plosive is still aspirated and shorten the vowel before them.
(d) Voiceless plosives also shorten the preceding voiced consonants such as [ m n l ŋ ] and vowel before these,
VD: belt / belt /
bump / bʌmp /
bank/ bæŋk/
bent/ bent/
(e) Unaspirated : voiceless plosives [ p t k ] will be unaspirated when preceded by the sound [ s ] for examples:
spy/spaɪ/
star / stɑː /
sky / skaɪ /
stamp /stæmp/
school/ skuːl /…
(f) Trường hợp ngoại lệ: key /kɪ/