Vowels are always voiced, and have no attack of their own. So, by this definition, yes, "y" and "w" can represent vowel sounds in words. Usually, when they do represent vowels, they are used in conjunction with one or more other vowels to create a polypthong: "w" represents "oo" and "y" represents "ee". For example, the word "way" is pronounced ... More @Wikipedia
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