8.3.56
सहेः साडः सः
Operational rule vidhi
The अपदान्त-सकार present in the 'साड्' form of the verb सह् is converted to षकार.
Word by word (padaccheda)
Target सहेः ṣaṣṭhī · ekavacanaTarget साडः ṣaṣṭhī · ekavacanaTarget सः ṣaṣṭhī · ekavacana
- Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
Full reading
सहेः साडः सः
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
Commentary
ष् is substituted for the स् in साह when this occurs in the form of साड (साट्).
Thus जलाषाट्, तुराषाट्, पृतनाषाट् ॥ साड् is derived from सह् by the affix ण्वि 7.2.63, there is vriddhi of the penultimate, the ह is changed to ढ 8.2.31. and the upapada is lengthened 6.3.137.
साढः सः would have been enough, for there is no other form साड् except this derived from सह्; why then the word सहेः is used in the sutra? There is another form साड् not derived from सह् ॥ Thus सह डेन वर्त्तते = सडः, सडस्य अपत्यं = साडिः ॥ He in whose name there is the letter ड is called सड; as मृड ॥
Why do we say 'in the form of साड्'? The rule will not apply when the form is साह, as जलासाहम्, तुरासाहम् ॥ Why do we say सः "for the स"? So that the आ of साड् may not be changed to cerebral : the ड् is already cerebral.
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.