7.4.81
स्रवतिशृणोतिद्रवतिप्रवतिप्लवतिच्यवतीनां वा
Operational rule vidhi
इ is optionally substituted for the final उ of a reduplicate of 1. स्रु 2. श्रु 3. द्रु 4. प्रु 5. प्लु and 6. च्यु when the semi-vowel is followed by a अ or आ in the Desiderative.
Word by word (padaccheda)
Target स्रवतिशृणोतिद्रवतिप्रवतिप्लवतिच्यवतीनाम् ṣaṣṭhī · bahuvacanaIndeclinable वा avyaya
- Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
- Indeclinable An avyaya such as च "and", वा "optionally", न "not".
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Full reading
स्रवतिशृणोतिद्रवतिप्रवतिप्लवतिच्यवतीनाम् वा
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
Commentary
इ is optionally substituted for the final उ of a reduplicate of 1. स्रु 2. श्रु 3. द्रु 4. प्रु 5. प्लु and 6. च्यु when the semi-vowel is followed by a अ or आ in the Desiderative.
Thus सिस्रावयिषति or सुस्रावयिषति; शिश्रावयिषति or शुश्रावयिषति; दिद्रावयिषति or दुद्रावयिषति; पिप्रावयिषति or पुप्रावयिषति; पिप्लावयिषति or पुप्लावयिषति; चिच्यावयिषति or चुच्यावयिषति ॥ All these are Desideratives of the Causatives of the above roots. Here though a letter like स्, श्, द् &c, intervenes between the semi-vowel and the preceding उ of the reduplicate, yet the substitution takes place owing to the express text of this sutra. In the preceding aphorism, the semi-vowel followed immediately after the उ of the reduplicate. The option of the present sutra is, therefore, an aprapta-vibhasha. The word अपरे is understood here also: therefore not in सुस्रूषति, शुश्रूषति ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.