सोपानम् ३०: विवक्षा, प्रातिपदिकार्थः & लिङ्ग-वचन-नियमः (२.३.४६)
Master the foundational station of nominal derivation: Unpack the 5 semantic grounds for the 1st case (२.३.४६ प्रातिपदिकार्थलिङ्गपरिमाणवचनमात्रे प्रथमा) and the dual taxonomy of nominal stems (१.२.४५ अर्थवत्... vs १.२.४६ कृत्तद्धितसमासाश्च).
प्रातिपदिक-संज्ञा & प्रथमा-विभक्तेः पञ्च-निमित्तानि
Why does a word take the 1st case (Prathamā)? Pāṇini’s foundational sūtra 'प्रातिपदिकार्थलिङ्गपरिमाणवचनमात्रे प्रथमा' (२.३.४६) dictates that the 1st case affix is not a random default, but an intentional operator attached for exactly 5 distinct semantic grounds:
Pure lexical substance, invariable adverbs, and stems with fixed inherent gender.
Stems with variable gender (Aniyataliṅga) where 1st case conveys specific gender.
Volumetric or container measure quantifying an unmeasured bulk substance.
Pure numerical count and quantifier concord.
पाणिनीय-पञ्च-सोपान-चक्रम् — The Complete 5-Stage Derivation Arc
विवक्षा & प्रातिपदिकम्
Intent & Stem Essence
२१ सुप् & कारक-विन्यासः
21 Sup & Kāraka Mapping
इत्-संज्ञा & 'तुस्माः' कवचम्
It-Compiler & Sup Armor
अङ्ग-कार्यम् & 'चोः कुः'
Stem Forge & Velar Shift
पद-कार्यम् & २१ रूपाणि
Pada & Living Forms