3.3.152 उताप्योः समर्थयोर्लिङ्

Word by word (padaccheda)

Right context उत- अप्योः saptamī · dvivacanaRight context समर्थयोः saptamī · dvivacanaSubstitute / term prathamā · 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").
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.

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Full reading

उत-अप्योः समर्थयोः लिङ्

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

Commentary

The affix लिङ् (Benedictive) comes after a verb in all tenses when the words उत and अपि , both having the same meaning, are in composition.
This excludes all the other tense-affixes. The meaning which is common both to उत and अपि is that of बाढम् 'assuredly, certainly, surely, really'. Thus उत कुर्यात् 'certainly he does'; अपि कुर्यात् 'assuredly he does' उताधीयीत 'certainly he studies (will study &c)'; अप्यधीयीत 'surely he studies &c'.

Why do we say 'when they mean certainly'? Observe उत दण्डः पतिष्यति 'will the stick fall'? अपि द्वारं धास्यति 'he shuts the door'. Here उत is employed in asking questions, and अपि with धा means 'to shut'. The option allowed by rule 3.3.141 ceases. Hereafter the Conditional (लृङ्) must invariably be used even in indicating Past action, when action is not completed, and there is reason for the employment of लिङ्(Potential). In indicating Future time, of course, लङ् must necessarily be employed as before. Henceforward, therefore, no option is allowed, but लृङ् must be employed where sutras 3.3.139 and 3.3.140 require it.

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