5.4.10 स्थानान्ताद्विभाषा सस्थानेनेति चेत्

Word by word (padaccheda)

Left context स्थानान्तात् pañcamī · ekavacanaSubstitute / term prathamā · ekavacanaWith / by सस्थानेन tṛtīyā · ekavacanaIndeclinable avyayaIndeclinable चेत् avyaya

Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.
With / by Tṛtīyā (3rd case): accompaniment or means.
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

स्थानान्तात् सस्थानेन चेत्

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

Commentary

The affix छ (ईय) is optionally added to a stem ending in स्थान if it is compounded with something with which another is made to take an equal place.
The word सस्थान means समानं स्थानमस्य 'whose place is the same" or तुल्य or equal. Thus पित्रा तुल्यः = पितृस्थानीयः or पितृस्थानः (पितुरिव स्थानमस्य whose place is that of a father). Similarly मातृस्थानीयः or मातृस्थानः, राजस्थानीयः or राजस्थानः ॥

Why do we say "when it means equal to". Observe गोस्थानम् "cow-shed" अश्वस्थानम् "stable". The word इति in सस्थानेनेति is for the sake of distinctness. The word सस्थान as a Bahuvrihi compound is the appropriate word to be taken here, and not when it is taken as a Tatpurusha compound like समानं च तत् स्थानं च ॥ The word चेत् "when", is a conjunction : and joins the two meanings.

The rule 5.3.9 occurring between this rule and 8th rule, both of which are optional, must be taken to be a nitya rule, as explained above. द्वयोर्विभाषयोर्नित्या विधयः ॥

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