This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Coptic Letters gathers the alphabet Egyptian Christians built by taking the Greek alphabet whole and adding seven further signs from the Demotic script for Egyptian sounds Greek had no letter for, the first stage of the Egyptian language whose vowels can be read directly off the page.
Every Greek derived letter keeps the numeral value it held in Greek, Alpha one, Iota ten, Khi six hundred, so a Coptic scribe writing a date used the same reckoning a Greek scribe would have; the seven Demotic additions, among them Fai, Hori, Janja, Khai and Kyima, carry no numeral value at all, since they entered the alphabet after the Greek series had already fixed the numeral series and had no place left in it. Several Greek letters, Gamma and Delta among them, found little native work in Egyptian and appear chiefly in Greek loanwords, personal names and the Greek liturgical formulae embedded in Coptic service books, so a manuscript's distribution of those letters is itself evidence for how much Greek vocabulary a given text carries. Hori, by contrast, is indispensable, standing behind Theta, Phi and Khi as the consonant those Greek letters compress with an h sound Egyptian had in abundance.
The alphabet is not quite one thing: Sahidic, the dialect of most surviving classical Coptic literature, counts thirty one letters, while Bohairic, the dialect that remains the living liturgical language of the Coptic Orthodox Church, keeps Khai as a thirty second, a difference between a dead literary register and a script still read aloud in church today.