7.2.89
योऽचि
Operational rule vidhi
य is substituted for the final of युष्मद् and अस्मद् before a case-ending which is not a substitute and which begins with a vowel.
Word by word (padaccheda)
Substitute / term यः prathamā · ekavacanaRight context saptamī · ekavacana
- Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.
- 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").
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Full reading
यः
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
Commentary
य is substituted for the final of युष्मद् and अस्मद् before a case-ending which is not a substitute and which begins with a vowel.
Thus त्वया, मया, त्वयि, मयि, युवयोः, आवयोः ॥ Why do we say 'beginning with a vowel'? Observe युवाभ्याम्, आवाभ्याम् ॥ If in the sutra 7.2.86, we read the anuvritti of हलि, we need not use अचि in the present sutra. For then this sutra will be a general (utsarga) aphorism, ordaining य before all non-substitute case-endings; and the sutra 7.2.86, will be considered an exception (apavada) to this, with regard to those case-endings which begin with a consonant, where आ will be ordained. In this view of the case, the use of अचि here is explanatory, Why 'when the ending is not a substitute'? Observe त्वद् गच्छति, मद् गच्छति ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.