A E I O U and sometimes Y, but also W?
When W occurs at or near the end of a syllable, it’s often part of yet another diphthong. Words like “brown” and “cow,” end with two vowels run together. First you have “aa” [as in “cat”] or “ah,” and then you have “oo.” So in these words, you could argue that W does indeed represent a vowel. On the other hand, maybe to you the word “cow” sounds like it ends with the consonant “wuh” instead of the vowel “oo.” Just as with the diphthong “oy,” phoneticians disagree. So my recommendation is just to say that the combination O-W represents the diphthong “ow,” and stop there, just like we did for the O-Y and the diphthong “oy.”
W also occurs at the end of words like “saw” and “drew.” These words don’t end with diphthongs; they end in the vowels “aw” and “oo.” By the same kind of reasoning we’ve already been using, it’s best not to call W a vowel or a consonant, but just to say that the letter combination A-W represents the vowel “aw,” and the combination E-W represents “oo.”
So to sum up, the only time you can truly say that W represents a vowel is in those rare Welsh borrowings, such as “cwm.” Y, on the other hand, gets to represent a vowel in many more words. It represents short I in words like “gym,” and either short I or long E in words like “happy.” It represents a diphthong in words like “by.”
And that’s our look at when Y and W represent vowels and consonants. Wow! Yay!