5.2.43
द्वित्रिभ्यां तयस्यायज्वा
Operational rule vidhi
The affix अयच् is optionally the substitute of तयप् after the words 1. द्वि and 2. त्रि.
Word by word (padaccheda)
Left context द्वित्रिभ्याम् pañcamī · dvivacanaTarget तयस्य ṣaṣṭhī · ekavacanaSubstitute / term अयच् prathamā · ekavacanaIndeclinable वा avyaya
- Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.
- Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
- 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".
Dotted words are technical terms. Hover or tap one to see its card.
Full reading
द्वित्रिभ्याम् तयस्य अयच् वा
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
तयस्य → अयच् / द्वित्रिभ्याम् optional
Replace tayasya with ayac when it comes after dvitribhyām, optionally. Inherited words (anuvṛtti) may add further conditions.
Commentary
The affix अयच् is optionally the substitute of तयप् after the words 1. द्वि and 2. त्रि।
As द्वाववयवावस्य = द्वयम् or द्वितयम्, त्रयम् or त्रितयम् 'a couple' 'a triad' 6.4.148.
The word तय is used in the sutra to indicate the sthanin or thing to be replaced. Had it not been used, the sutra would have run thus द्वित्रिभ्यामयज् वा "ayach optionally comes after dvi and tri". Here ayach would have become a separate affix, instead of being a mere substitute. Where is the harm in its being a separate affix? Then the word त्रयम् or द्वयम् will not form their feminine in ङीप्; but अय being taken as sthanivat to तय (1.1. 56), the affix ङीप् which by 4.1.15, applies to तय, applies to अय also. Thus we have त्रयी गतिः ॥ Moreover by 1.1.33, words ending in तय are declined as Pronouns optionally before nominative plural termination. By the rule of sthanivat adesa 1.1.56, the words ending in अय will also be Pronouns. As द्वये or द्वयाः त्रये or त्रयाः ॥ The च् in अयच् is for accent, showing that the substitute 'aya' differs in accent from the sthani taya.
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.