Mongolian Pa: The Letter That Marks a Borrowing

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.