I was wondering if anyone could explain why some words are spelt the same but pronounced slighlty differently?
For example 'sun' is pronounced differently in 'unsung' compared to in 'asunder'.
Any ideas?
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The context can make a big difference.

The n, for example, is pronounced differently when it is followed by a g or k or c or x or q, compared with when it is followed by other letters.

unsung, asunder.

CalifJimThe n, for example, is pronounced differently when it is followed by a g or k or c or x or q, compared with when it is followed by other letters.

unsung, asunder.
Heh, now you are forcing me to ask you about some interesting stuff!
How do you say "increase"? /ɪnkris/ or /ɪŋkris/?
How about uncommon? With /nk/ or /ŋk/?
This has to do with assimilation, and I have been struggling with this damn feature for quite a while. It is very difficult, if not impossible for me, to "hear" assimilation while listening to English, unless it's done in very slow speech too.
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The part -sun- is actually pronounced the same way in each of the examples you have given Emotion: nodding
The are zillions of such examples (e.g. the different sounds in eat and great). English is very irregular when it comes to its pronunciation rules. As far as I know, the reason would be the language's complicated history - it started it off as a Germanic language with influences from the surrounding Scandinavian and Celtic and possibly other languages. The English language from this period (5th - 12th c.) is called Old English. It later underwent serious changes due to what the invasion of William the Conqueror in 1066 brought along, namely the French language, which, unlike English, is a Romance language. The language from this period is referred to as Middle English. To sum up, you can find traces of various influences in nowadays English that are reflected in the various ways of spelling and pronuncation.
 CalifJim's reply was promoted to an answer.
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 Kooyeen's reply was promoted to an answer.
There are a number of reasons. In some cases syllable breaks cause pronunciation differences. Consider:
  • creature /kri.chr/
  • creation /kri.ai.shn/
In other cases stress patterns in a particular language dictate how words are pronounced. Consider the 'i' in the following words.
In your above example, the 'ng' is actually a digraph, i.e., a grouping of letters representing once sound. The sound /ng/ is not the same as /n/. Other digraphs include:
  • th - which can be pronounced as a soft 'th' as in 'thigh' or a hard 'th' as in 'thy'
  • ch
  • sh
Another reason is history. The 'gh' in 'right' came from the 'ch' sound in German /rIxt/, but we've lost that sound, so the 'i' sound changed to replace the lost sound: /rait/.

Another reason is that English words come from a number of different languages or even borrowed a different times from the same language so sometimes inherit different pronunciations.
  • chief /chif/ came from the French 'chef' in the 14th or 15 century
  • chef /shEf/ came from the French 'chef' in the 19th century

Because english lack a one to one correspondence, this mean that it is not as in spanish that we have one letter one sound.

The reason is because english comes from differents languages

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