2.3.19
सहयुक्तेऽप्रधाने
Operational rule vidhi
When the word सह 'with', is joined to a word the latter takes the 3rd case, when the sense is that the word in the 3rd case is not the principal but the accompaniment of the principal thing.
Word by word (padaccheda)
Right context सहयुक्ते saptamī · ekavacanaRight context अप्रधाने saptamī · ekavacana
- 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").
Full reading
सहयुक्ते अप्रधाने
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
Commentary
When the word सह 'with', is joined to a word the latter takes the 3rd case, when the sense is that the word in the 3rd case is not the principal but the accompaniment of the principal thing.
Ex. पुत्रेण सहागतः पिता 'the father has come with the son.'
The same will be the result with the synonyms of सह as, पुत्रेण सार्द्धं 'with the son'. So also when the word सह is understood, as Panini himself uses in 1.2.65 वृद्धो युना &c.
Why do we say 'when not the principal.' Observe, शिष्येण सहोपाध्यायस्य गौः.
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.