अस्य च्वौ

Operational rule vidhi

Long ई is substituted for the final of अ or आ of a Nominal stem, before the Adverbial affix च्वि -- अभूततद्भावे कृभ्वस्तियोगे सम्पद्यकर्तरि च्विः (5.4.50).

Word by word (padaccheda)

Target अस्य ṣaṣṭhī · ekavacanaRight context च्वौ saptamī · ekavacana

Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
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").

Dotted words are technical terms. Hover or tap one to see its card.

Full reading

अस्य च्वौ

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

Commentary

Long ई is substituted for the final of अ or आ of a Nominal stem, before the Adverbial affix च्वि -- अभूततद्भावे कृभ्वस्तियोगे सम्पद्यकर्तरि च्विः 5.4.50।
As शुक्ली करोति, शुक्ली भवति, शुक्ली स्यात् ॥ खट्वी करोति, खट्वी भवति and खट्वी स्यात् ॥

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.