In my teach myself Greek mode, I've had an open question that seems not to be resolving itself. Why do some texts ive 7 diphthongs and others 8 - the discrepancy being hu ?
My best guess is that true Biblical Greek grammars do not have the eta/upsilon diphthong because it does not appear in the text. You might be seeing the difference between a Biblical(narrow) grammar and a classical(wide) grammar.
I think Alan is most likely correct. I find no instance of the diphthong ηυ in the NT and find the combination ηυ in some alternate text of the Göttingen LXX where I don't believe it would be considered a diphthong (ἠ̈υ for ἠΰτε). This could be explained by the fact that Koine is largely based on the Attic dialect. Note Smyth's comment
"Ionic has ηυ for Attic αυ in some words (Hom. νηῦς ship)."
Smyth, Herbert Weir. Greek Grammar, §5D, p 9. Harvard University Press, © 1984.
thanks guys.
