Conscience has a /ʃ/ sound in the middle of the word.

Science has a /saɪ/ sound, not a /ʃ/ sound.

What rule makes conscience have the /ʃ/ sound and what rule makes science have the /saɪ/ sound?

They are spelled very similarly.

Your help would be greatly appreciated.

  • 2
    Because they're different words. They do supposedly derive from the same root, but they separated in late Latin, then hopped to French, before being adapted into English.
    – Hot Licks
    Commented Apr 16, 2020 at 17:06
  • Sound differently? Are you using sound as a verb? Otherwise it sounds rather different to standard grammar.
    – David
    Commented Jul 9, 2020 at 18:47

1 Answer 1


The reason boils down to English stress patterns.

Science is stressed on its first syllable and the vowel/diphthong in stressed syllable is strong so it's pronounced /ˈsaɪ.əns/.

Another example is scintillating which is stressed on the first syllable so it's pronounced /ˈsɪntɪleɪtɪŋ/.

On the other hand, the monosyllabic prefix con- bears the primary word stress so when it's added to the word science, the primary stress from the word science moves to the prefix con- therefore conscience is stressed on the first syllable and is pronounced /ˈkɒnʃ(ə)ns/ not /ˈkɒn.saɪ.əns/ (the vowel in unstressed syllable often reduces).

The /ʃ/ sound is due to Yod-coalescence.

Other examples are:

  • Extension -> /ɛkˈstɛnʃ(ə)n/.
  • Social -> /ˈsəʊʃ(ə)l/.

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