Sou ⲋ

Sou is the sixth sign of the Coptic alphabet and writes no sound whatever. It exists because Coptic took over the Greek alphabetic numeral system, and that system had a problem in its sixth position. The oldest Greek alphabet contained a letter, digamma, which fell out of use as a sound in most Greek dialects long before the classical period, but its numeral value of six survived in the counting series because dropping it would have shifted every value after it. Greek scribes went on writing a sign in that place, which in the manuscript tradition merged with the ligature called stigma.

Coptic inherited the arrangement complete, so Coptic alphabet charts list sou between ei and zeta, and Coptic scribes wrote it whenever they needed the figure six. No Coptic word contains it. The sign is a clean demonstration that an alphabet and a numeral series are two systems that happen to share a set of shapes, and that the two can come apart. Greek needed two further signs of the same kind to cover ninety and nine hundred, koppa and sampi, and those too are numeral signs rather than letters, appearing in Coptic manuscripts where a number requires them but never in a Coptic word. Coptic charts vary in whether they print them in the alphabet at all, which is a matter of editorial convention rather than of dispute about the script.

Numbers do a great deal of work in a Coptic manuscript. Quires are numbered so a binder can assemble them, folios and pages are numbered, chapters and scriptural divisions are numbered, dates are written out, and the Coptic calendar with its thirteen months requires figures constantly. All of this was done with letters rather than with a separate set of digits, in the alphabetic system Coptic took from Greek: the first nine letters count the units, the next nine the tens, the next nine the hundreds. That arrangement requires twenty seven signs, and the Greek alphabet in ordinary use has only twenty four, which is why sou and two further numeral only signs exist.

Coptic scribes distinguished a letter used as a figure by drawing a stroke above it, so a reader met no ambiguity even where a numeral stood in the middle of running text. The same convention marks the abbreviated sacred names Coptic inherited from Greek Christian book practice, and the two uses are told apart by context. The system has one further consequence that shaped how numbers were thought about across the Christian and Jewish east: because every letter carried a value, every written word carried a total. Greek writers called the practice of summing those totals isopsephy, and Hebrew tradition calls the equivalent gematria. Coptic possessed the same mechanism by inheritance, and the alphabet chart with sou in its sixth place is where the mechanism starts.