Mongolian Na and What Dots Do in This Script

Dots in the traditional Mongolian script are a repair rather than a foundation. The inherited alphabet did not have enough distinct shapes for the sounds Mongolian distinguishes, and rather than invent new letterforms the tradition added marks to existing ones. The dental nasal is separated from a vowel by one dot; the voiced velar is separated from the back class velar by dots; other pairs are separated the same way. The device is familiar from elsewhere in the same family of scripts, since Arabic and Syriac both use points to multiply a small stock of shapes into a larger alphabet, and Mongolian inherited the habit along with the letters.

What is peculiar to Mongolian is how readily the dots are dropped. In Arabic the points are obligatory in ordinary text and their omission is an archaism; in Mongolian the omission is normal in handwriting and common in print, and the script is designed to survive it. That tells you where the tradition places the burden of reading. The written form is a strong hint rather than a complete specification, and the reader is expected to bring the language with them. It is also why transcribing a Mongolian manuscript is a task requiring knowledge of Mongolian rather than only knowledge of the alphabet.