Mongolian U ᠤ

U writes a rounded back vowel and is the fifth letter of the alphabet. It shares its written shape completely with the letter before it, so that in ordinary writing there is no difference at all between o and u, and the two are kept apart only in the reader's knowledge of the word. The alphabet nevertheless lists them as separate letters, recites them separately, and encodes them separately at U+1823 and U+1824, which tells you that the tradition regards them as two letters that happen to look alike rather than as one letter with two readings. The distinction is real in the language even where it is invisible on the page. Both belong to the back class of the vowel harmony, so neither helps a reader decide which class a word belongs to; that job falls to the consonants and to the suffixes.

In the sequence of positional forms, u behaves exactly as o does, with an initial form introduced by an opening stroke, a medial form attached to the spine, and a final form drawn out below the last letter of the word. Learners of the script are usually taught the o and u pair together and taught immediately that the pair cannot be resolved from the shape, which is a useful early lesson in how much of this writing system depends on the reader.

The Mongolian alphabet has fewer vowel signs than the language has vowels, and the reason is historical. Its ancestor was an abjad, a script built for a Semitic language in which vowels were largely left unwritten and a single letter, waw, served for the rounded vowels and for the labial glide together. Sogdian and then Old Uyghur adapted that inventory as they went, and each adaptation improved the fit without completing it. Mongolian received a vowel system built for other languages and made it work rather than rebuilding it, which is the normal fate of a borrowed script.

Other scripts in the same position took the other road: Greek reassigned unused Phoenician consonant letters to vowels and produced a full alphabet, and Coptic added seven signs from Demotic for sounds Greek could not write. Mongolian added letters too, ten of them, but for consonants met in foreign words rather than for the vowels its own language distinguishes. That choice tells you something about what the script was for. Its users were not troubled by a written form that a Mongolian speaker could read without difficulty, and they were troubled by the impossibility of writing Sanskrit, Tibetan and Chinese names correctly in a religious literature that was full of them. The alphabet was extended where the need was felt, and left alone where it was not.