Mongolian Ya and the Letters That Sit Between Consonant and Vowel

Alphabets are usually taught as a list of vowels and a list of consonants, and the glides are where that tidy division fails. The palatal glide and the labial glide are made like vowels and behave like consonants, and every alphabet has to decide what to do with them. The Semitic abjads from which this script ultimately descends used the same letters for both jobs, writing the glides as consonants and later pressing the same signs into service as vowel letters, which is how the ancestors of these Mongolian letters acquired their vowel readings in the first place. The vowel i and the palatal glide are one sign in that history; the rounded vowels and the labial glide are another.

Mongolian inherited the arrangement and kept it, listing four vowels and a glide where the ancestry had one letter, and writing them with shapes that overlap accordingly. It is worth knowing this when comparing the Mongolian alphabet with its relatives, because a table that lines up the letters one to one will always break at the glides, and the break is not an error in the table. It is the record of one sign being asked to do several jobs over two thousand years. The same reasoning explains why the alphabet's list and the alphabet's shapes do not correspond one to one. A recited list names the letters the tradition counts; the shapes on a page record only what the tradition thought worth distinguishing, and the two have never been the same inventory.