a is from the letter aleph (-> greek alpha) which represents a glottal stop o is from the letter `ayn which represents a voiced pharyngeal fricative (and also

a is from the letter aleph (-> greek alpha) which represents a glottal stop o is from the letter `ayn which represents a voiced pharyngeal fricative (and also `ayn is the word for "eye" in Semitic languages, hence the shape of the letter o) e is from he, representing the sound h as in house (the letter h comes from the letter Ḥet, which spells an unvoiced pharyngeal fricative) i is from yod (-> greek iota), the consonant sound of y u is from waw, the consonant sound of w y is also descended from waw, via Semitic -> Greek -> Latin Basically, the Greeks and Romans wrote vowels using the letters that spelled consonants that were useless in their native language (not a lot of pharyngeal fricatives in Europe)