8.2.76
र्वोरुपधाया दीर्घ इकः
Operational rule vidhi
The उपधा letter of a रेफान्त or a वकारान्त पद which also has a धातुसंज्ञा becomes दीर्घ if that letter belongs to the इक् प्रत्याहार.
Word by word (padaccheda)
Target र्वोः ṣaṣṭhī · dvivacanaTarget उपधायाः ṣaṣṭhī · ekavacanaSubstitute / term prathamā · ekavacanaTarget ṣaṣṭhī · ekavacana
- 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.
Dotted words are technical terms, dashed ones pratyāhāras (names for classes of sounds or affixes). Hover or tap one to see its card.
Full reading
र्वोः उपधायाः
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
र्वोः उपधायाः →
Replace rvoḥ upadhāyāḥ ikaḥ with dīrgha. Inherited words (anuvṛtti) may add further conditions.
Commentary
A penultimate इ or उ is lengthened, when the र् or व् of a root can stand at the end of a word.
Thus गीः, धूः, पूः, आशीः ॥ These are all examples of roots ending in र् ॥ Of roots ending in व्, examples will be given in the next sutra.
Why have we used the word 'penultimate'? Observe अबिभर् भवान्, here the इ of the reduplicative syllable is not to be lengthened.
Why do we say 'of इक् vowels'? So that the अ of भ in the above example अबिभर् may not be lengthened.
The word धातोः 'of a root' is understood here also. Therefore इ and उ are not lengthened in अग्निः, वायुः ॥
The word पदस्य is understood here also, therefore, not here, गिरौ, गिरः ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.