phonological patterns lettER, horsES, commA

Vowels in unstressed final syllables vary between  , often in harmony with the preceding vowel in suffixes like –ness, -ity, -es. This yields pairs of possible pronunciations like  , where the [ə] -form occurs after most vowels and the -form occurs after high-front vowels. That said, vowel harmony is only suggestive, not controlling, in such situations. Unstressed final –er and –a are of course distinguished by r-coloring in StAmE.