Today, someone asked me if the pronunciation of the "c" in "exacerbate" is an /s/ or a /z/. In fast speech, it seems indistinguishable if I substitute /z/ for the /s/ , which is the standard dictionary pronunciation).

Are both pronunciations acceptable? I did some digging and discovered that between two vowel sounds, the phoneme is voiced (reason, cousin, teasing) , but I'm not sure if this is a hard and fast rule.

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    Have you looked up exacerbate in a dictionary? Seems they have /s/. Reason, cousin, tease are all pronounced /z/ not /s/, as a dictionary will tell you - it's not a question of them having an /s/ which is sometimes voiced, they have a /z/. But there are no hard and fast rules linking spelling and pronunciation.
    – Stuart F
    Oct 17, 2023 at 21:31
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    Haha, I'd be more triggered by the "ex" at the start being pronounced "eggs". But I call these sound changes "sandhi", and whether I like them or not in english, they are a standard phenomenon in language, and can't be called "wrong" (but can be called "irritating"!)
    – ralph.m
    Oct 17, 2023 at 21:33
  • @StuartF looked it up and saw it was /s/, but yeah… I wonder..
    – meepyer
    Oct 17, 2023 at 21:35
  • No matter how fast I say "exacerbate," it's fairly clear that the sound is S and distinguishable from Z.
    – cruthers
    Oct 17, 2023 at 21:42
  • Well, it ain't exazerbate. zero is not sero.
    – Lambie
    Oct 17, 2023 at 21:57

1 Answer 1


In the usual pronunciation of exacerbate, c is pronounced as /s/.

There is absolutely no rule saying the phoneme /s/ is replaced with /z/ between two vowel sounds.

The words "reason, cousin, teasing" are examples of the letter (not phoneme) ⟨s⟩ being used to represent the sound /z/ between two vowel letters. That is common, but it is not a rule either: to list just a few exceptions, goose, crease, cease always have /s/ and glucose, basic, evasive usually have /s/.

Voiceless phonemes can sometimes have some phonetic voicing (this occurs not just in English but in all kinds of languages). Maybe that is why you find that it doesn't sound different in fast speech if you use /s/ or /z/ in exacerbate.

  • Could you link me to a good site that talks about phonetic voicing for voiceless phonemes?
    – meepyer
    Oct 18, 2023 at 19:30
  • @meepyer: Sorry, I'm not sure I know of one. I think I was basing my comments partly on the article A voice for the voiceless: Production and perception of assimilated stops in French which is mainly about French and is largely technical. There are some other articles like that I've read but I don't know of a good introduction to the concept.
    – herisson
    Oct 18, 2023 at 20:56
  • Thanks! No worries. It’s been a while since I took any phonetics classes but it’s still helpful to know.
    – meepyer
    Oct 20, 2023 at 4:48

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