Upsilon and the Vowels Coptic Writes with Two Letters

Coptic does not have a letter for every vowel it pronounces. It has the Greek vowel letters, and for the u sound it uses a digraph, the two letters ou written in sequence, exactly as Greek did by the period when Coptic was formed. That is a straightforward inheritance rather than a compromise, since Greek itself had long written the sound that way, but it has consequences for reading. A beginner who has learned that ou is worth seventy and upsilon four hundred meets the two letters together writing a single vowel and has to recognise that a digraph is one unit. The same difficulty arises with the diphthongs Coptic spells out letter by letter, which is why the two dots above a vowel matter: they are the signal that the letters are not to be taken together.

All of this sits inside the larger point about what the Greek alphabet gave Egyptian. The older Egyptian scripts wrote no vowels at all, so the question of how to spell a u never arose. Coptic had to answer it, and answered it by taking the Greek solution whole, along with the Greek reading aids that make the solution workable. The seven letters brought in from Demotic answer a different set of questions, about consonants Greek could not write, and the alphabet as it stands is the sum of both answers.