झलां जश् झशि

Operational rule vidhi

A झल्-letter is converted to a corresponding जश्-letter when followed by a झश् letter.

Word by word (padaccheda)

Target ṣaṣṭhī · bahuvacanaSubstitute / term prathamā · ekavacanaRight context saptamī · ekavacana

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.
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

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

As a rewrite rule (sketch from case endings)

→ /

Replace jhalām with jaś when jhaśi follows. Inherited words (anuvṛtti) may add further conditions.

Commentary

In the room of झल् letters, there is substitution of जश् letters, when झश् letters follow.
A mute letter is changed to a sonant non-aspirate mute, when a sonant mute follows it.

This is the well-known rule of softening the hard letters. Thus लभ् + ता = लब्धा, so also लब्धुम्, लब्धव्यम्; दोग्धा, दोग्धुम्, दोग्धव्यम्; बोद्धा, बोद्धुम्, बोद्धव्यम् ॥

Why do we say झशि, 'when a jhas follows'? Observe दत्तः, दत्थः, दध्मः ॥

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