The pronunciation guide shows that the IPA symbol for υ, υι, and οι is /y/ like a rounded "ee" sound. I'm struggling with this sound, I've spent some time learning french and the french "u" also has an IPA symbol of /y/ but it's closer to the u in "cute" or "ew" than the "ee" sound. So I guess there's two questions. How should I be pronouncing these vowels and diphthongs, and how do you pronounce it when there's two identical vowel sounds in a row like in υιοι. Thanks!
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Good questions Kyle! There was actually variation with words like υἱός and υἱοί in the Koine period as well.
The evidence suggests that the below pronunciations were all valid:
υἱός = [yˈo̞s], [yiˈo̞s]
υἱοί = [yˈy], [yiˈy]
We know this from spellings like υος and υειος, the first showing the contraction with the [i] vowel and the latter showing the preservation of the [i] vowel.
Hope this helps!