अचः परस्मिन् पूर्वविधौ

This sutra consists of three words:- अचः genitive of the pratyahara अच् meaning 'of a vowel,' and means an adesa which takes the place of a vowel. The words adesa and sthanivat are understood and are to be supplied from the preceding sutra . The second word is 'parasmin' loc. sing. of 'para' meaning 'in the subsequent.' The locative has the force of 'on account of or by reason of.' The third word is purva-vidhau loc. sing. of purva-vidhi meaning 'a rule applicable to a preceding thing.' The whole sutra thus comes to mean that an adesa which replaces a vowel, becomes sthanivat (like vowel), provided that the substitution has been occasioned on account of something following and when a rule is to be applied to anything preceding such an adesa.

Thus there is an affix called णिच् the actual affix being इ; the other letters ण् and च् being इत्. The peculiarity of every affix having an indicatory ण् is to cause the vriddhi of the penultimate अ; (sutra 7.2.116) as पच + इ = पाचि. Now in forming the denominative verb from the word पटु, we have to add the affix णिच्. Thus पटु + इ ; but before nich, the उ of पटु is substituted by a 'lopa' or blank, and this blank takes the place of the vowel उ of पटु and becomes sthanivat by force of the present sutra . The result of becoming sthanivat is that though the अ of पटु is really a penultimate and ought to be vriddhied before 'nich' it is not so, the lopa-substitute not allowing the अ to be regarded as penultimate, and thus we have the form पटि the present tense third person singular of which is पटयति. The equation being पट् + ० + इ, the zero preventing the अ of पट् from becoming penultimate. So also in the word अवधीत्, the aorist (लुङ्) of वध. Thus अ + वध + ईत् = अ + वध् +० + ईत्. Here, the अ of वध is elided by 6.4.48. (when an ardhadhatuka affix follows there is elision of the short अ of that which ends in short अ;) this elision is thus caused by something which follows (parasmin.) Now there is a rule (VII. 2. 7.) which declares 'vriddhi is optionally the substitute of a laghu अ preceded by a consonant when सिच् (aorist) follows.' However in the present case the zero is considered as sthanivat, and prevents the application of sutra 7.2.7; otherwise we get the form अवाधीत् which is inadmissible.

Similarly बहुखट्वा + कप् = बहुखट्वकः । Here, the short अ is the substitute of the longआ of खट्वा by 7.4.15; because of the subsequent (parasmin) affix 'kap'. However, the word बहुखट्व will not be considered as a word ending in a short vowel, for the purposes of the application of rule 6.2.174, (the udatta accent falls on the last vowel but one of a word that ends in a short vowel and is the last member of a bahuvrihi compound followed by the affix kap). On the contrary the short अ is regarded as sthanivat to long आ. Thus बहुख॑ट्वकः.

It is needless to say that this rule applies only to vowel adesa, therefore, where an adesa replaces a consonant, the previous sutra 1.1.56 has its scope and prevents its being sthanivat. Thus there is a krit affix called ल्यप्, the real suffix being य, the ल् and प् being diacritical letters. Before this य the verb आगम्(to come) loses it म्, and lopa or blank takes the place of म्. Here then lopa or blank is an adesa and म् a consonant is sthani.

Now there is a rule which says 6.1.71, that before krit affixes having an indicatory प्, the letter त is added after verbs ending in light vowels. Now in आगम्, when म् is omitted, the अ of ग becomes final; and therefore a त् is required before य (which is a पित्त् affix). Thus we have आगत्य.

But had lopa or blank become sthanivat to म् then the अ of ग would have remained penultimate as it was when it was आगम्; and no त् would have been required. But it is not so.

Similarly in forming the word प्रश्नः. Thus प्रच्छ् + नङ् 3.3.90 प्रश् + नङ् 6.4.19. Here, श् is substituted for छ्; this will not be sthanivat to छ्; though this substitute is caused by something that follows (parasmin). Were it to be sthanivat, there would come the augment तुक् (त्) by 6.1.73.

Similarly अक्राष्टाम्, the aorist of कृष्. Thus अ + कृष् + सिच् + ताम् = अ + कृष् + ० + ताम् 8.2.26. Here the स् is elided on account of what follows, but still the lopa substitute here is not sthanivat for the purposes of 8.2.41. Had it been sthanivat, ष् of कृष् would be changed into क्.

Moreover this rule applies where a vowel is changed on account of something which follows (parasmin). Therefore, where the change has not been occasioned by anything subsequent, the adesa (though of a vowel) is not sthanivat. Thus the words युवजानिः and बधुटीजानिः.

The word युवजानिः is a bahuvrihi compound of युवति and जाया, meaning 'he who has a young wife.' In forming this compound, the आ of या is replaced by नि (tech. निङ्) by sutra 5.4.134. This नि will not be sthanivat to आ, as it is not caused by anything which follows. Had it been regarded as sthanivat, the य् could not be elided by 6.1.66 ('there is elision of व and य when any consonant except ह् or य् follows'). Thus, युवजाया + नि = युवजाय् + ० + नि 5.4.134 = युवजानिः 6.1.66.

Similarly the word वैयाघ्रपद्यः, 'a descendant of व्याघ्रपात्' also illustrates this rule. व्याघ्रपाद् is a bahuvrihi compound of व्याघ्र and पाद, meaning 'whose foot is like that of a tiger.' Now the final अ of 'pada' is elided in such compounds by 5.4.138. This lopa substitution is not caused by anything that follows, therefore, this lopadesa will not be sthanivat for the purposes of the application of sutra 6.4.130 ('पत् is the substitute of the word पात् when part of an inflective base ending in the word पाद् and entitled to the name of Bha. I. 4. 18'). Therefore, व्याघ्रपाद् + यञ् 4.1.105 = वैयाघ्रपद्यः. Had the lopa been like the original, there could not have been the substitution of 'pad' for 'pad.'

Similarly the word आदीध्ये, Ist per. sing. atm. present tense of the root दीधी 'to shine.' Thus आदीधी + इट् = आदीधी + ए 3.4.79. This change of इ into ए is not caused by anything that follows, hence ए is not sthanivat to इ, for the purposes of the application of rule 7.4.53 ('the finals of didhi and vevi are elided when an affix beginning with य or इ follows'). Had ए been sthanivat, the final ई would have been elided.

Similarly an adesa though of a vowel, and even though occasioned by a subsequent something, would not be sthanivat, if there is not the application of a rule to something that precedes the adesa (purva-vidhi). If the rule is to be applied to something subsequent to the adesa; it will be applied to the exact adesa without considering what was the letter which the adesa had replaced. It is only when a rule is to be applied to a prior object, that it becomes important to consider whether the adesa is sthanivat or not. Thus the vocative case of गो is हे गौः । The vocative is formed from the nominative case 2.3.49. The nominative of गो is formed by changing ओ into औ and adding the case termination स्. Here the adesa औ, replaces ओ, on account of the subsequent termination स्. Now there is a rule applicable to vocative cases which declares that the final स् is dropped after short vowels ए and ओ 6.1.69.

Now is the औ of गौ to be regarded as sthanivat to ओ, which it replaces; for the purposes of this rule of elision of finals? If so, the consequence would be that the final स् would have to be dropped in the vocative. But it is not so. Because the rule 6.1.69, which ordains the dropping of स् after short vowels and ए and ओ applies to a letter, which is not anterior to the adesa औ, but to one which follows it, and consequently there being no purva-vidhi here, the final स् is retained and we have the vocative गौः ।

Similarly the word बाभ्रवीयाः, 'the pupils of Babhravya.' The word बाभ्रव्य is derived from बभ्रु in this wise. बभ्रु + यञ् (IV. I. I05) = बाभ्रो + यञ् 6.4.146 and 7.2.117 = बाभ्रव् + यञ् 6.1.79 = बाभ्रव्यः. From this is formed बाभ्रवीय in this wise :- बाभ्रव्य + छ् 4.2.114 = बाभ्रव्य + ईय 7.1.2 = बाभ्रव्य् + ईय 6.4.148 = बाभ्रव् + ईय 6.4.150. Here, had the substitute अव् which replaced the ओ of बाभ्रो, been sthanivat to ओ, rule 6.4.150 ('there is elision of the य of a taddhita affix coming after a consonant, when long ई follows'), could not have applied. But this substitute अव् is not sthanivat for the purposes of rule 6.4.150, in as much as that rule does not apply to any letter that precedes the substitute अव्, but to the very letters of the substitute itself.

Similarly the word नैधेयः, which is evolved from the root धा, in this wise नि + धा + कि 3.3.92 = नि + धा + इ (1. 3. 8)= नि + ध् + ० + इ 6.4.64 = निधि. Let us then form a secondary derivative from the word निधि applying ढक् 4.1.122, the whole of which affix is replaced by एय 7.1.2. Thus निधि + एय = निध् + एय6.4.148 = नैधेय 7.2.118. Here, the lopa substituted for the आ of धा by 6.4.64 is not sthanivat for the purposes of the application of (IV. I. 122) by which the affix ढक् is added. Rule 5.1.122 says, 'dhak is added to a word ending in इ, provided it be a word containing two vowels.' Now निधि ends in इ and contains two vowels; but if the lopa were sthanivat to the elided आ, then it would be a word of three syllables. That is however not so; because the rule enjoining the affix ढक् is not applicable to anything preceding the lopadesa, but is enjoined with regard to something after this substitution.,