क्षय्यजय्यौ शक्यार्थे

Operational rule vidhi

The words क्षय्य and जय्य are considered to be derived, in the meaning of (respectively) 'the one that is capable of being destroyed' and 'the one that is capable of being won over'.

Word by word (padaccheda)

Substitute / term क्षय्य- जय्यौ prathamā · dvivacanaRight context शक्यार्थे 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").

Dotted words are technical terms, dashed ones pratyāhāras (names for classes of sounds or affixes). Hover or tap one to see its card.

Full reading

क्षय्य-जय्यौ शक्यार्थे

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

Commentary

In क्षय्य and जय्य there is substitution of अय् for ए only then when the sense is that of 'to be possible to do'.
The roots क्षि and जि before the affix यत् 3.1.97 assume these forms when meaning to be able to do the action denoted by the verb. As शक्यः क्षेतुं = क्षय्यः (क्षि + य = क्षे + य); so also जय्यः ॥ Why do we say when meaning "to be possible to do"? Observe क्षेयं पापं, जैयो वृषलः ॥ Here the meaning is that of 'necessity'.

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.