There's a phenomenon called Trisyllabic laxing where the vowel in a stressed syllable is shortened if two (or more) syllables follow. If the stressed vowel is in at least* the penultimate syllable (third-last syllable of the word) then it must be lax. It's fairly common in English and mostly occurs when Latin suffixes are attached to a word.
- Profane, profanity --- [prəˈfeɪn] -> [prəˈfæn.ə.ti]
- Sincere, sincerity --- [sɪnˈsɪə] -> [sɪnˈser.ə.ti]
- Impede, impediment --- [ɪmˈpiːd] -> [ɪmˈped.ɪ.mənt]
- Divine, divinity --- [dɪˈvʌɪn] -> [dɪˈvɪn.ə.ti]
- Michael, Michaelmas --- [mʌɪkl] -> [mɪkəlməs]
- Profound, profundity --- [prəˈfaʊnd] -> [prəˈfʌn.də.ti]
- Provoke, provocative --- [prəˈvəʊk] -> [prəˈvɒk.ə.tɪv]
The above words have a very regular pattern of vowel change which is summarised below:
- [eɪ] -> [æ]
- [ɪə] -> [e]
- [iː] -> [e]
- [ʌɪ] -> [ɪ]
- [aʊ] -> [ʌ]
- [əʊ] -> [ɒ]
However, in some cases, trisyllabic laxing appears to take place when it should not have done so. For example, Christ [kraɪst] vs Christmas [ˈkrɪs.məs], even though the stress syllable in Christmas is followed by one syllable yet it gets laxed. In such cases, the anomaly is caused by later sound changes. Christmas was a three syllable word (stress on first syllable) when Trisyllabic laxing applied. (Full explanation here)
In some words, it seems to have applied within Latin. That's actually what I'm asking.
- Decide, decision --- [dɪˈsʌɪd] -> [dɪˈsɪʒ(ə)n], comes from Latin decisionem
- Collide, collision --- [kəˈlʌɪd] -> [kəˈlɪʒ(ə)n], comes from Latin collisionem
- Divide, division --- [dɪˈvʌɪd] -> [dɪˈvɪʒ(ə)n], comes from Latin divisionem
- Reside, residue --- [rɪˈzʌɪd] -> [ˈrɛzɪdjuː], from Latin residuum
- Did trisyllabic laxing apply to these words within Latin (before entering English)?
- Is trisyllabic laxing active in Latin?