Mongolian Pa ᠫ

Pa writes the voiceless bilabial stop, and it is the eleventh letter of the alphabet. Its position in the language is unusual: native Mongolian words do not begin with it, so an initial p is a reliable sign that a word came from somewhere else. The sound does occur inside native words, but the constraint at the start of a word is firm enough to be diagnostic, and readers use it that way.

Unicode encodes pa at U+182B. Its written shape is closely related to that of the voiced bilabial stop before it in the alphabet, which is what one would expect of a letter that had to be provided for a sound the inherited alphabet handled less fully than Mongolian required. The pattern recurs throughout the script: where a distinction was needed and no separate shape was available, the tradition modified a shape already present rather than inventing a new one. That conservatism is a large part of why the alphabet remains legibly related to its Uyghur and Sogdian ancestors after eight centuries. A reader who knows what the letter signals gets useful information from it before reading the word. Words of Sanskrit and Tibetan origin in the Buddhist literature begin with this letter constantly, and their presence on a page is itself a fair indication of what kind of text it is.

The Mongolian religious vocabulary is heavily borrowed, and the borrowing came in layers. Buddhist terms entered by more than one route: some through Uyghur, which had a Buddhist literature before the Mongols did, some directly from Tibetan, and some from Sanskrit by way of Tibetan. Each route left a different phonetic shape on the same word, so the atlas of Mongolian Buddhist terminology contains doublets that are historically one word arriving twice. The alphabet was pressed hard by this. Sanskrit distinguishes aspirated from unaspirated stops and voiced from voiceless in a four way system that Mongolian does not have; Tibetan spelling preserves clusters that Mongolian cannot pronounce; Chinese contributes syllables with no Mongolian analogue at all.

The response was to add letters, ten of them at the end of the alphabet, and beyond those a further set of signs, encoded in Unicode under the name Ali Gali, for writing Sanskrit and Tibetan in full. From the sixteenth and seventeenth centuries the script carried a very large Buddhist literature in Mongolian, including a translation of the Kangyur, the canonical collection of the Buddha's discourses, and that literature is the main reason the extended apparatus exists at all.