The Mongolian script or Hudam Mongolian script, was the first of many writing systems created for the Mongolian language and the most successful until the introduction of Cyrillic to Mongolia in 1946. With minor modification, the classic vertical script is used in Inner Mongolia to this day to write both Mongolian and the Evenki language.
The Mongolian vertical script was developed as an adaptation of the Uyghur script to write the Mongolian language. It was introduced by the Uyghur scribe Tatar-Tonga, who had been captured by the Mongols during a war against the Naimans around 1204. There were no substantive changes to the Uyghur form for the first few centuries, so that, for example, initial yodh stood for both [dʒ] and [j], while medial tsadi stood for both [dʒ] and [tʃ], and there was no letter for [d] in initial position. Mongolian sources often distinguish the early forms by using the term Uyghurjin script Mongolian for Uyghur style script). Western sources tend to use this term as a synonym for all variations of the Mongolian script.
The middle period of the development of Mongolian extended from the seventh and eighth to the fifteenth and sixteenth centuries. The Mongolian language of this period is divided into southern. eastern and western dialects. The principal monuments of the middle period are: in the eastern dialect, the famous Secret History of the Mongols, monuments in the square script, materials of the Chinese-Mongolian glossary of the fourteenth century, and materials of the Mongolian language of the middle period in Chinese transcription, etc.; in the western dialect, materials of the Arab-Mongolian and Persian-Mongolian dictionaries, Mongolian texts in Arabic transcription, etc. The main features of the period are that the vowels ï and i had lost their phonemic significance, creating the i phoneme; intervocal consonants Y/g, b/w had disappeared and the preliminary process of the formation of Mongolian long vowels had begun; the initial h was preserved in many words; grammatical categories were partially absent, etc. The development over this period explains why Mongolian script look like a vertical Arabic script (in particular the presence of the dots system).
Eventually, minor concessions were made to the differences between the Uyghur and Mongol languages: In the 17th and 18th centuries, smoother and more angular versions of tsadi became associated with [dʒ] and [tʃ] respectively, and in the 19th century, the Manchu hooked yodh was adopted for initial [j]. Zain was dropped as it was redundant for [s]. Various schools of orthography, some using diacritics, were developed to avoid ambiguity.
Mongolian is written vertically. The Uyghur script and its descendants—Mongolian, Oirat Clear, Manchu, and Buryat—are the only vertical scripts written from left to right. This developed because the Uyghurs rotated their Sogdian-derived script, originally written right to left, 90 degrees counterclockwise to emulate Chinese writing, but without changing the relative orientation of the letters.
Characters take different shapes depending on their initial, medial, or final position within a word. In some cases, there are additional graphic variations which are selected for better visual harmony with the subsequent character.
The alphabet fails to make several vowel (o/u, ö/ü, final a/e) and consonant (t/d, k/g, sometimes ž/y) distinctions of Mongolian that were not required for Uyghur. The result is somewhat comparable to the situation of English, which must represent ten or more vowels with only five letters and uses the digraph th for two distinct sounds. Sometimes, ambiguity is avoided, because the requirements of vowel harmony and syllable sequence usually determine the right choice. Moreover, as there are few words with an exactly identical spelling, actual ambiguities are rare for a reader who knows the orthography.