After n and ṣ , the ṇ is the substitute of n , when they occur as component letters in the same word.,
These letters must be parts of the same pada or word, one being the 'occasion' for the application of the rule as regards the other. As आस्तीर्णम्, विस्तीर्णम्, अवगूर्णम् ॥ So also after ष; as कृष्णाति, पुष्णाति, मुष्णाति ॥
The letter ष् is included in this aphorism for the sake of subsequent sutras : for न् will be changed into ण् when preceded by ष् by rule 8.4.41 of this Chapter, as well.
Why do we say \when occurring in the same word?\ Observe अग्निर्नयति, वायुर्नयति ॥
Vart:- So also after the letters ऋ ॥ As तिसृणाम्, चतसृणाम्, मातॄणाम्, पितॄणाम् ॥
This vartika may well be dispensed with: because the र in the sutra is the common sound र which we perceive both in र and ऋ; and so the र will denote both the vowel ऋ and the consonant र. See contra. 8.2.42. Objection:- But if even this be so, the letter ऋ has three parts, its first part is a vowel, in the middle is the र् sound of a quarter matra, and a vowel sound at the end. This vowel-sound will intervene between the र-sound and the subsequent न, and will prevent the application of the sutra, hence the vartika is valid ?
Answer:- This vowel-sound will be no intervention, because it will be included in the exception अट् of the next sutra. Objection:- The vowel-sound at the end of ऋ is not a full vowel of one matra, but is of half-matra, being only a fragment of ऋ, and hence is not included in the pratyahara अट्, it has no separate स्थान or प्रयत्न or homogeneity with any vowel. Hence this vowel-sound will prevent the application of this rule. Answer:- The ण change, however, does take place in spite of such intervention of a fragment of a letter, as we know from the jnapaka of 8.4.39. In the kshubhnadi list there we find नृनमन as an exception, implying that न is generally changed to ण after such a fragmentary interposition. Or we may take नृनमन as a jnapaka, that after the letter ऋ also the ण change takes place.,