If you know anything about music, you probably know solfège. For a major scale, one can sing the notes using the syllables do-re-mi-fa-sol-la-ti-do. This system was made popular by The Sound of Music. The syllables originate from a Latin hymn Ut queant laxis, from the words that fall on the associated pitches of the scale.
These syllables are used for major scales, but alternations are made when singing minor scales. The natural minor, for example, is sung do-re-me-fa-sol-le–te-do. So on three notes, instead of [i] or [a], we are to sing [e] instead. As far as I can tell, these particular syllables aren’t associated with any hymns, and changing the words in Latin doesn’t seem to do anything interesting to the meanings.
One argument about why solfège changes this way is that this system emphasizes what notes are different in the minor scale, grouping them together by using the same vowel. Except that “re” also has [e], and that’s not a minor interval (even if it’s still present in a minor key).
A colleague suggested that solfège exhibits “arbitrary morphological alternation”, and a discussion ensued as to whether the lowering of the vowel is somehow “sadder” sounding than a high vowel. High vowels are associated with small things, as a sort of sound symbolism, and maybe an argument could be made regarding the “happy” sound of the major key and the associated high vowels. That doesn’t explain why “la” gets changed to “le”, though.
We might just have another interesting way that music is like language. It seems to make sense, generally, but exhibits irregularities which are hard to explain (but we try anyway!).