Phi: The Coptic Letter (Value 500), from Greek Phi

Phi is the twenty second letter of the Coptic alphabet and carries the numeral value five hundred; Coptic Orthodox usage names it fi. In classical Greek it wrote an aspirated p, a p with a following breath, and by the Roman period the sound had become an f. Coptic took over the later value, which is another instance of the general rule that Coptic borrowed the Greek alphabet as it was actually being spoken and written in Roman Egypt rather than as a classical textbook describes it. Phi belongs to the group of Coptic letters that also serve as compressions, standing for the sequence pi plus hori just as theta stands for tau plus hori and khi for kappa plus hori. Coptic may write either the single letter or the two, and manuscripts differ along dialect and workshop lines, so the preference is usable evidence when a book has to be placed.

Phi also appears in the fused definite article that turned so many Egyptian nouns into fixed names, and through Greek those names reached Latin and the modern languages of Europe. In the numeral series phi is worth five hundred, sitting in the rank of hundreds with the Greek value it has always had. The doubling of the f sound between phi and the Egyptian letter fai is not a defect in the alphabet but a record of how it was assembled. Coptic acquired phi as part of a complete Greek series in which it had once written an aspirated p, and acquired fai separately because Egyptian needed an f of its own. Where a word takes each of them is therefore a piece of etymological information sitting openly on the page, visible to a reader who knows the two layers of the vocabulary and invisible to one who does not.