Phonemics vs Phonetics
The pronunciation of a sound may vary depending on its position in a word and the sounds that precede or follow it. Phonetic transcription shows these variations whereas phonemic transcription doesn't.
For example, in the word ‘contestant’ /kÉ™nˈtestÉ™nt/ the first /t/ sound is aspirated, which means there is an extra puff of air and a slight delay before the following vowel sound. In contrast, the final /t/ sound is glottalised, which means the air is partially stopped in the larynx.
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Although these sounds are technically different, they can’t change the meaning of a word. Therefore, the listener interprets them as the same phoneme and the same symbol is used. Phonemic transcription places these symbols between slanted brackets.
These variations in pronunciation are known as allophones, and each phoneme represents a range of possible allophones. In most cases phonemic transcription is sufficient because the rules concerning when to use each allophone are already known or learnt.
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However, in some cases it may be necessary to transcribe each individual sound in a word. In this case, phonetic transcription is used.
Phonetics uses additional symbols to transcribe the exact pronunciation of a sound and places them between square brackets. So, the word ‘contestant’ is transcribed phonetically as [kə̃nˈtÊ°É›s.tə̃nË€t].