The standard pronunciation of "is" is /ɪz/. I looked up its etymology and saw that its pronunciation in Middle English was /iːs/, with /s/. In Old English, it was also /iːs/

On the other hand, the word "this" is pronounced as /ðɪs/ in standard Englishes, with /s/. And its etymology suggests that it was also /θis/ with /s/ in Old ENglish. It is constant, its pronunciation did not change.

So why did the /s/ change to /z/ in "is"? Or why didn't the /s/ change to /z/ in "this"?

(I just noticed that the Old English pronunciation of "this" has /θ/ but now it has /ð/ but I am not asking about that. Ignoring that would be better. My main question is about the ending "s").

  • 2
    Your link for the OE pronunciation of "is" is to an OE word "is" meaning "ice", not to the word "is". (In fact, the same is true of your ME link, although in that case if you scroll down, "is" meaning "is" is there too and has /s/ but with a shorter /i/ in the transcription.)
    – rjpond
    Commented Nov 7, 2020 at 9:25
  • They are different parts of speech. The verb forms is, was and has are pronounced like more regular verbs when they take an 's' such as talks, says, does etc. But this is pronounced as nouns like thesis, analysis, stasis etc. Commented Nov 7, 2020 at 9:48
  • @rjpond I thought it was the verb "is". Pardon my ignorance, I didn't even read the full entry.
    – user119042
    Commented Nov 7, 2020 at 10:00

2 Answers 2


In Old English, "s" at the end of a word was usually unvoiced /s/. In modern English it is often voiced (but depends on the environment and the sound preceding it etc). Additionally, it historically originated as "ist", which we would pronounce with /s/ even in modern English if it was a modern English word. The -st- can also be found in German "ist" and (a more distant relative) Latin "est".

  • 2
    I don't see why you talk about ist. The question is why it isn't unvoiced.
    – Colin Fine
    Commented Nov 7, 2020 at 14:02
  • The question was about the history as much as, or more than, the present. Its history illustrates why it began as unvoiced. And it's plausible that when the t first began to be dropped, the unvoiced value was retained partly because of the history - although it is also the case that final s was regularly unvoiced in OE anyway, which is not the case in modE. So the question is partly about how or why that particular convention changed, which I don't know. That said, after posting in the comments, I was urged to post an answer. I don't claim it to be a complete or perfect one though.
    – rjpond
    Commented Nov 7, 2020 at 15:05

Really, the answer is "because that's how it is", as with most "why" questions about languages.

But there is a strong (though not universal) tendency in English for final fricatives to be voiced after an unstressed vowel.

As well as is, you have as and of, as well as the ubiquitous -es ending.

This may not have full stress, but it is generally stressed relative to is.

Counter-example: us (but the s is often voiced in parts of Yorkshire).

  • 'Us' pronounced with a /z/ is increasingly common in other British accents as well, especially in the construction "us all".
    – Void
    Commented Nov 7, 2020 at 14:30
  • If a word often occurs at the end of a phrase, or anyhow before a pause, the tendency for its final fricative to become voiced may be more pronounced.
    – Deipatrous
    Commented Sep 19, 2023 at 9:39
  • @Deipatrous, do you think is has a tendency to occur in that position? It does sometimes, certainly, but far more often not, in my view.
    – Colin Fine
    Commented Sep 19, 2023 at 9:42

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