8.2.74
सिपि धातो रुर्वा
Operational rule vidhi
द् or रु may optionally be substituted for the स् of a root, , before the personal ending सि (स्) when such स् stands at the end of a word.
Word by word (padaccheda)
Right context सिपि saptamī · ekavacanaTarget धातोः ṣaṣṭhī · ekavacanaSubstitute / term रुः prathamā · ekavacanaIndeclinable वा avyaya
- Right context Saptamī (7th case): "when X follows", the operation applies to what precedes (1.1.66 तस्मिन्निति निर्दिष्टे पूर्वस्य). Also a condition or domain ("in the sense of").
- Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
- Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.
- Indeclinable An avyaya such as च "and", वा "optionally", न "not".
Dotted words are technical terms. Hover or tap one to see its card.
Full reading
सिपि धातोः रुः वा
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
धातोः → रुः / सिपि optional
Replace dhātoḥ with ruḥ when sipi follows, optionally. Inherited words (anuvṛtti) may add further conditions.
Commentary
द् or रु may optionally be substituted for the स् of a root, , before the personal ending सि (स्) when such स् stands at the end of a word.
Thus अचकास् त्वम् or अचकात् त्वम्, अन्वशास् त्वम् or अन्वशात् त्वम् ॥ For the रु is first substituted visarjaniya, which is then changed to स् ॥
The word धातुः is employed in the sutra for the sake of the subsequent sutras : so also the word रु ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.