When would one need सिद्धान्तकौमुदी ?

Ms. Irene Gelstian posted a query, “Please help me understand when should one consult the full version, and when the abridged version is sufficient.” By ‘full version’ she meant सिद्धान्तकौमुदी and by ‘the abridged version’ लघुसिद्धान्तकौमुदी. Here is my deliberation.

Just a look at the contents of the two books also brings out some major differences. For example second chapter in सिद्धान्तकौमुदी is परिभाषाप्रकरणम्. There is no such chapter itself in लघुसिद्धान्तकौमुदी  So, if one wants to understand what परिभाषा is, then one needs to study it only in सिद्धान्तकौमुदी.
As per my understanding, परिभाषाः are premises, which are inherent in the structure of the book.
For example there is  सूत्रम् – विप्रतिषेधे परं कार्यम् (पा. 1-4-2). In the instance of dilemma, go by the latter.
  • An example of dilemma is अच्सन्धिः of इ + इ, say इति इच्छा
  • If one should go by इको यणचि (6-1-77) the संधि should be इत्यिच्छा.
  • But by अकः सवर्णे दीर्घः (6-1-101) the संधि would be इतीच्छा.
  • So we have a dilemma – should इति इच्छा be इत्यिच्छा or इतीच्छा ?
  • विप्रतिषेधे परं कार्यम् resolves the dilemma saying “go by the latter.” Between (6-1-77) and (6-1-101) the latter is (6-1-101). Hence, इतीच्छा only.
  • So विप्रतिषेधे परं कार्यम् is the परिभाषा, the premise behind पाणिनि’s sequencing of the सूत्राणि in अष्टाध्यायी.
  • But this premise विप्रतिषेधे परं कार्यम् does not extend all across. It extends only up to (8-1-74). Its application beyond (8-1-74) is stopped by पूर्वत्रासिद्धम् (8-2-2).
    • For example, what should be संधि of ते अज्ञानम् ?
    • By एचोऽयवायावः (6-1-78) तयज्ञानम्
    • By लोपः शाकल्यस्य (8-3-19) तेऽज्ञानम्
    • Going by विप्रतिषेधे परं कार्यम् it should be only तेऽज्ञानम्. However since application of विप्रतिषेधे परं कार्यम् does not extend beyond (8-1-74), तयज्ञानम् as per एचोऽयवायावः (6-1-78) is also valid.
So, a totally different answer to the query “when should one consult the full version” is, “go by अष्टाध्यायी itself.” Even the full version सिद्धान्तकौमुदी may not explain many such nuances, much less, the short or abridged version लघुसिद्धान्तकौमुदी.
One may get intrigued by the सूत्राणि listed in different chapters, both in लघुसिद्धान्तकौमुदी and सिद्धान्तकौमुदी. For example अच्सन्धिप्रकरणम् in both lists the सूत्रम् – झलां जश्झशि (8-4-53). Prima facie, the वर्ण-s dwelt upon in this सूत्रम् are all हलः. Why then is this सूत्रम् in अच्सन्धिप्रकरणम् at all ?
Having said all this, it seems, first of all, one needs to ask oneself, how deep one wants to go. Looks like, the query seeks clear identification as “लघुसिद्धान्तकौमुदी will take one as much deep, सिद्धान्तकौमुदी that much deeper and for further depth only अष्टाध्यायी itself.” I don’t think any such identification exists.  Particular study on hand will itself dictate which book to refer.
शुभमस्तु !