Can /ɪ/ and /ə/ be used interchangeably in unstressed syllables?

[fruitninja]

E.g. "believe", "delete", "define"....I looked up the word "define" in dictionaries. One says /də-'fain/, the other one says /dɪ-'fain/. So, can I use either /ɪ/ or /ə/ for these words ? I tried listening to speakers, but the unstressed syllable is pronounced so fast; sometimes, it's hard to tell which one.

 

[Skrej]

It very common for the vowels in the unstressed syllables in English to revert to the /ə/, which is known as a schwa. This is especially true when speaking rapidly.

It's critical that you have the correct vowel sound in a stressed syllable (in terms of comprehension), but if your unstressed syllable vowels are a little off, it doesn't make as much difference for this reason.

English is stress-timed, meaning the stressed syllables are uttered at roughly equal intervals, and the unstressed syllables are shortened to maintain that pacing. One way we shorten them is to revert to a schwa vowel, because it's short and quick to utter.

 

[CommuniKate]

That's an interesting question. I don't think so. Is there an example you're thinking of?

 

[jutfrank]

They can (such as in the examples you give -- delete/define/believe) but not always.