The schwa has many spellings. The /aɪ/ diphthong is spelled <iCe>, <y> and <i> in levis, and occurs in the letter name I.
This is a contrast between a short vowel which is always unstressed and a diphthong. It is not in itself a problem for learners. A number of the words with schwa are weak forms of grammar words.
Interesting pairs include:
The density figure is 0.3%. The set makes 19 semantic contrasts giving a loading of 86%.
a I acclamation acclimation Allah ally alumna alumni carbon carbine carbons carbines coalman coalmine coalmen coalmine datum daytime 'em I'm labour layby labours laybys levers levis philosophers philosophize signallers signalize starlet starlight the thy to tie topography typography turban turbine turbans turbines westerners westernize
John Higgins, Shaftesbury, December 2009