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...
I'm not sure that's the (sole) rule for "Y as vowel". It acts as a vowel in "fly", "spy", and a few other words. And it seems pretty darn dipthong-like when clustered among vowels, eg "voyeur", "vying".
The word "eye" is an interesting one. It seems to be only vowels, based on pronunciation.
> a vowel when it's between two consonants, and a consonant when it's not.
Not a hard rule, honestly.
Some Indian languages exhibit a blurring of sorts with Ye- sounds. E.g., in Telugu, the word for 'How' is 'yela', which is often also pronounced as 'ela'. TBF, Telugu also blurs Ve-/We- sounds similarly.
The first rule of English is that the rules aren't really rules because they are broken all the time. Makes sense when you consider English is just an amalgamation of Scandinavian, Germanic, French, Latin, etc words and rules. Hard to have rules when you mix a half dozen completely different rulesets into one.
