Mongolian Oe and the Front and Back Series Side by Side

Set out as a table rather than as a recited list, the Mongolian vowels form a small and regular system. The back series holds the open vowel a and the two rounded vowels o and u. The front series holds the open vowel e and the two rounded vowels written o and u with umlauts. The vowel i stands outside both and is neutral. Every native word draws from one series, and every suffix has a back form and a front form and presents whichever matches. The written script conveys only part of this. It marks the difference between the open vowels at the start of a word and not inside it, and it does not mark the difference between the members of either rounded pair at all.

What it does mark, and marks consistently, is enough for a reader who knows the language, because harmony makes the missing information recoverable. This is worth stating carefully rather than treating the script as merely deficient. A writing system carries some of the information in a language and leaves the rest to the reader, and where the line falls differs from script to script. Arabic and Hebrew leave most short vowels unwritten. English leaves stress unmarked. Mongolian leaves the rounded vowels undifferentiated and marks the consonant alternations that harmony governs. In each case the omission is safe because the language makes it predictable.