by Qimmik » Tue Oct 01, 2013 4:39 pm
Paul's understanding is the same as mine.
At some point the original diphthong ει merged with long ε (the result of contraction or compensatory lengthening), and the merged sound, a long closed ε, continued to be written as a digraph, ει, even though it was a monophthong.
Similarly, the original diphthong ου merged with long ο (the result of contraction or compensatory lengthening), and the merged sound, a long closed ο, continued to be written as a digraph, ου, even though it was a monophthong. Further sound changes occurred, and ου (/o:/) was raised to /u:/, while υ was raised to /y/.
Thus, ει and ου resulting from contraction or compensatory lengthening were never pronounced as diphthongs, in contrast to the original diphthongs ει and ου, which at one time were pronounced as diphthongs.
οι resulting both from an original diphthong and contraction remained a diphthong at least until after the classical period, sometime after which οι merged with ι. So the history of οι is different--there is no reason to distinguish between spurious and genuine οι.
In the classical period, eta represented a different sound from ει, specifically, a long open /e:/. Similarly, omega represented a long open /o:/.
Eventually eta, ει, οι and υ merged with ι, and vowel quantity was lost.