षत्व-तुकोर् असिद्धः

The word असिद्ध means not-accomplished i. e. the operation caused by its having taken effect is not produced. The word asiddha always debars operations dependent upon this adesa, and gives scope to the operations dependent upon the general rule ( असिद्धवचनमादेशलक्षणप्रतिषेदार्थमुत्संगलक्षणभावार्थं च ॥) Thus कांऽसिचत् here स is not changed to ष ॥ The equation is thus exhibited : कस् + असिचत् = कर् + असिचत् (the स changed to र by 8.2.66) कंउ + असिचत् (उ being substituted for र by 6.1.113) = को + असिचत् (अ + उ = ओ 6.1.87) = कोऽसिचत् (ओ + अ = ओ 6.1.109). Now applies our sutra. By 8.3.59, स coming after ओ required to be changed into ष, but here the single-substitute ओ is considered to be non-effective for this purpose. Similarly कोऽस्य, योऽस्य, कोऽस्मै, यौऽस्मै ॥ Similarly in अधीत्य there is the addition of त् by 6.1.71, though actually preceded by a long vowel. That long vowel had resulted from the ekadesa of ई for इ + इ, and this ekadesa is considered as if non-effective for the purposes of तुक् augment. Similarly in प्र + इ + तुक् + य = प्रेत्य. Here also अ + इ = ए is considered asiddha.

Vart:- Prohibition must be stated in the case of samprasarana, the Locative singular case-ending is ङि (इ), and the Ist person singular Atmanepada affix इट् ॥ Of vocalisation we have the following : शकहूष् = शकान् ह्वयति, then we add क्विप्, before which there is vocalisation of व्, this उ combining with in the following आ becomes उ ekadesa: as शकहा + क्विप् = शकह्उआ + ० (VI. I. I5) + शकहु (VI. I. 108). The Locative plural is formed by सु : शकहु + सु = शकहूषु (the lengthening taking place by 6.4.2). Here स is changed to ष the ekadesa उ for उ + अ not being considered asiddha. So also परिवीषु (परि + ष्ये + क्विप् = परि + व्इए + क्विप् = परिवि, add सु)॥ Of the affix ङि we have:- वृक्ष + इ = वृक्षे, add छत्रम्, then the single substitute ए being considered not asiddha we have वृक्षेच्छत्रम् or वृक्षेछत्रम् ॥ Of the affix इट् of Ist Person Atmanepada we have अपचे + छत्रम् = अपचेच्छत्रम् or अपचेछत्रम् ॥ In both these cases we optionally add तुक् by (VI. I. 75) - (VI. I. 76), by considering the ekadesa 6.1.87 as to have taken effect, and making the finals दीर्घ or long. Here the ekadesa is not asiddha and therefore तुक् is optional and not compulsory.,