Mongolian E and How Vowel Harmony Organises a Word

Vowel harmony is the single fact about Mongolian that a reader of the script has to hold in mind, and the letter e is where it becomes visible. The vowels divide into a back series and a front series, with i standing outside and belonging comfortably to either. A native word takes its vowels from one series throughout, so a word containing e will not also contain a, and a suffix arriving at the end of that word will present its front form rather than its back one. This is not decoration. It is the mechanism that lets an ambiguous script stay readable, because a shape that could be two different vowels is settled by the company it keeps. The same principle reaches into the consonants: the velar written for back class words is not the velar written for front class words, and the choice between them is governed by the vowels around them rather than by anything the speaker chooses.

Harmony of this kind is common across the languages of northern Asia, and it is one of the features that first led scholars to group Mongolian with Turkic and Tungusic languages, a grouping that has since been argued about at length without being settled. What is not in dispute is the pattern itself, which any page of traditional Mongolian writing displays, and which the alphabet was reorganised around when it was borrowed.