Nna: The Retroflex Nasal, Mostly Produced by Rule

Nna is the fifteenth consonant of the varnamala, the retroflex nasal and the closing member of the third varga. In classical Sanskrit most of its occurrences are produced by a rule rather than inherited in the word: a dental n is converted into this retroflex nasal when certain retroflex or r-like sounds occur earlier in the same word, and the conversion applies across the boundaries inside a compound as well as within a simple word. The grammarians state the rule and its conditions with a precision that has made it a standard example in modern discussions of how Panini's system works, since the conditions involve intervening sounds that block or permit the change and the interactions are far from trivial. The practical consequence for a reader is that the letter marks a place where a rule has operated.

Seeing it in a written form is information about the shape of the underlying word, and reading it back to the dental is part of the analysis a student of the grammar is trained to perform. That gives the letter a different standing from most of its neighbours: it is not simply a sound the language happens to contain but a visible trace of the language's own machinery. The rule that produces the sound carries its own name in the grammatical tradition and is among the most discussed single rules in the Ashtadhyayi, because the conditions under which an intervening sound blocks the change are intricate and interact with one another. Modern work on Panini has formalised it repeatedly, and it is a standard test case for any account of how his system of rules is meant to operate.