Earlier quoted context omitted.
We were taught in grade school that the vowels were "A, E, I, O, U....and sometimes Y" without any real explanation. I count that as our first lesson about the convoluted complexities of the English language.
Y is used as a vowel when it's between two consonants, and a consonant when it's not. A word like "Synchronize" uses y as a vowel, but a word like "Yellow" uses it as a consonant. Honestly, it's more vowel-like then consonant-like in every case I can think of, so maybe that rule is kind of weak, and it should be counted as a vowel all of the time...
The word "eye" is an interesting one. It seems to be only vowels, based on pronunciation.