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Finite rhymes with 'my time'. Infinite rhymes with 'minute' (as in seconds, minutes, hours and not minute, micro, small).

Why are i's in finite and infinite pronounced differently?

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    I don't think there is a rule per say. There are some other words that change pronunciation when you add a prefix/suffix, such as famous and infamous, or photograph and photographer. This Q&A brings up some good points about how pronouncing infinite with a hard "i" sound is difficult. – James May 9 '15 at 7:45
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    I'm voting to close this question as off-topic because in my opinion, asking how come a word is pronounce the way it's pronounced is about etymology and etymology is off-topic on ELL. (And migrating this question to ELU would make it a duplicate.) – Damkerng T. May 9 '15 at 20:46
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    @James you misspelled per se. I wouldn't normally be quite this picky, but this is English Language Learners, after all. – phoog Sep 7 at 18:25
  • "finite rhymes with 'my time'". Now I'm really confused. – Eric Duminil yesterday
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Finite is pronounced ['faɪnaɪt] while infinite is pronounced [ˈɪnfɪnɪt].
So why is the vowel in the first syllable of 'finite' different from the vowel in the second syllable of 'infinite'?
It's probably because of Trisyllabic Laxing. It's a process whereby a tense vowel (as /aɪ/ in 'finite') is reduced to a lax vowel when two (or more) syllables follow.

Examples:

  • Serene /sɪˈrn/ -> serenity /sɪˈrɛnɪti/
    The tense vowel /i:/ in the second syllable of 'serene' gets reduced to /ɛ/ when we add more syllables.
  • Divine /dɪ'vn/ -> divinity /dɪ'vɪnɪtɪ/
    The tense vowel /aɪ/ gets reduced to a lax vowel /ɪ/.
  • Profane /prəˈfn/ -> profanity /prəˈfæn.ə.ti/
    The tense vowel /eɪ/ gets reduced to a lax vowel /æ/.

And the most common example is pronounce/pronunciation.

  • Pronounce /prəˈnns/ -> pronunciation /prəˌnʌn.siˈeɪ.ʃ(ə)n/

There are many different cases of Trisyllabic Laxing. Finite - infinite is one of them.

When we add the prefix in- to the word 'finite', the primary stress from the FI of 'finite' moves to the prefix 'in-'. And now the stressed syllable is followed by two syllables, so the tense vowel /aɪ/ in the root word ('finite', not the prefix 'in-') gets reduced to a lax vowel /ɪ/.

Pronounce/pronunciation is pretty much the same as finite/infinite.

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  • I thought of trisyllabic laxing (and that accounts for infinity) but it does not account for finite/infinite, as they both have just one syllable after the "fin". – Colin Fine Oct 12 at 18:31
  • @ColinFine: Perhaps the primary stress is relevant here? – Void Oct 12 at 18:32
  • Maybe. It's like intimate (both verb and adjective) and instigate, but neither of those have a version without in-. I pronounce indirect with /ʌɪ/ (it's usually somewhat reduced, but not to /ɪ/ - but the OED tells me that some people do use that pronunciation), but there is only secondary stress on the in-, not primary in that word. – Colin Fine Oct 12 at 19:14
  • @ColinFine: After giving it some more thought... 'Infinite' comes from Latin infīnītus which was pronounced [[ĩː.fiːˈniː.t̪ʊs]], stressed on the penult. But in English, we usually stress the antepenult, so something happened while borrowing it from Latin, though I'm not entirely sure (I don't know anything about Latin). Also compare 'potent' and 'impotent'. – Void Oct 14 at 18:12

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