6.1.39
वश्चास्यान्यतरस्याम् किति
Operational rule vidhi
Before the tense-affixes of the Perfect that have an indicatory क (1.2.5), for the य् of वय् may optionally be substituted a व्.
Word by word (padaccheda)
Substitute / term वः prathamā · ekavacanaIndeclinable च avyayaTarget अस्य ṣaṣṭhī · ekavacanaRight context अन्यतरस्याम् saptamī · ekavacanaRight context किति saptamī · ekavacana
- 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".
- 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").
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Full reading
वः च अस्य अन्यतरस्याम् किति
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
अस्य → वः / अन्यतरस्याम् किति
Replace asya with vaḥ when anyatarasyām kiti follows. Inherited words (anuvṛtti) may add further conditions.
Commentary
Before the tense-affixes of the Perfect that have an indicatory क 1.2.5, for the य् of वय् may optionally be substituted a व्।
Thus ऊयतुः or ऊवतुः, ऊवुः or ऊयुः ॥ According to Patanjali, the phrase वश्चास्य of this sutra could have been dispensed with; this much would have been enough:- अन्यतरस्या किति वेञः ॥ Thus वे + अतुम् = वा + वा + अतुस् = ववतुः and ववुः (the vocalisation being prohibited). In the alternative:-वा + अतुस् = उ +अतुस् = उ + उवङ् + अतुस् 6.1.77 = ऊवतुः, ऊवुः ॥ Here there is vocalisation. In the case of वय् substitute, the य is never vocalised, so we have ऊयतुः, ऊयुः ॥ Thus all the three forms have been evolved without using वश्चास्य ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.