27 Οriginally υ represented the sound that was afterward
written ου. The two close vowels, ι and original υ, when followed by a vowel, became
consonantal, like our consonants y and w respectively; the same change occurred in Latin, and often occurs in
English. The earliest Greek had these two consonants; the latter survived in some
dialects in the classical period, and was represented by Ϝ, called vau, or (from its shape) δί-γαμμα digamma. But in
Attic both had disappeared before 5ΟΟ B. C. Thus arises the rule:
The close vowels ι and υ often disappear between two vowels. See [135](file:///x:/Departments/Classics_Texts/schoolgrammarofa00goodrich_porson/HTML%20Files/Chapter-135.html).
- a. In observing sound changes the original diphthong ει
(from ε + ι must be distinguished from the digraph ει, which
represents the simple sound ε (anciently = French é) lengthened. So also the original diphthong oυ (from ο + original υ)
must be distinguished from the digraph oυ, which represents
the simple long sound of original ῡ. The rule in
[27](file:///x:/Departments/Classics_Texts/schoolgrammarofa00goodrich_porson/HTML%20Files/Chapter-027.html) applies to
the true diphthongs, before they coalesced in pronunciation
with the simple ει and ου.