After whatsoever there is an affix enjoined, whether verbal or crude-form, that which begins therewith in the form in which it appears when the affix follows it, is called an aṅga 'Inflective base'.,
The words of this sutra require some explanation. Yasmat after whatsoever; pratyaya-vidhih compound of pratyaya meaning an affix and vidhih, a precept i.e. a rule enjoying an affix; tadadi, I. S. that which begins therewith pratyaye 7. S. = in a pratyaya i.e. when a pratyaya follows (1. 1.) is called a base.
After whatsoever there is an affix enjoined, whether it be a verbal root (Dhatu) or a nominal base (pratipadika), the word-form having that as its beginning, is called an anga, with regard to the affix that follows. The word yasmat is used in the aphorism to point out the thing named, as anga; because the word tadadi follows it. This defines the word anga. The word 'base' is thus a relative term with regard to its affix. Thus कृ + ता = कर्ता he will do हर्ता he will lose. करिष्यति, हरिष्यति. Here because the root कृ and हृ gets the name अंग they are gunated by 7.3.84. Similarly because उपगु &c. get the name Anga, their vowel is vriddhied in औपगवः &c.
The words kri hri are anga with regard to the affix ta &c. उपगु + अण् = औपगवः; कापटवः. Here upagu and kapatu are anga with regard to an. Similarly कृ + स्य + वः = करिष्य + वः = करिष्यावः. Here the whole word form Karishya is regarded as anga, and as such the short a is lengthened by 7.3.101; because though the affix vah is enjoined after the word kri, the form which begins with kri i.e. karishya will also be called anga when the affix is to be added. The word tadadi, therefore, has been used in the sutra, to make the definition of Anga applicable to the forms which a word may assume after taking the intermediate affixes like sya &c., or नुम् before the final affixes. Thus कुण्ड + नुम् + इ = कुण्डन् + इ = कुण्डानि 7.1.72 and 6.4.8 kunda + num + i = kundan +i = kundani, bowls. Here the whole form kundan is called anga, and as such it lengthens its vowel before the case-affix i by 6.4.8.
Why have we used the word pratyaya? Without it the rule would have run thus :- 'After whatever there is anything enjoined &c., is called Anga.' Then in स्त्री + इयती = स्त्रयती. Here sandhi of vowels is enjoined between ई + इ = ई. If स्त्री was here an Anga, then its last last vowel would have been replaced by इयङ् 6.4.77, the form being स्त्रियियति.
Why have we used the word विधि ? Had we omitted it the rule would have run thus:-- \After whatsoever there is an affix, whether root or pratipadika is Anga.\ Thus in दधि अधुना, though the affix adhuna is placed after the word dadhi, it is not enjoined by any rule, and the word दधि is not called anga. Had it been so called, then the इ of dadhi should have been elided by rule 6.4.148.
The word pratyaya has been repeated twice in this sutra in order to show that when an affix is elided, the term anga will not apply to what stood before it. Thus in the compound word स्त्रियै + अर्थं = स्त्र्यर्थं for the sake of the woman. Here in forming the Tatpurusha compound the dative case-affix after the word स्त्री has been elided, for as a general rule case-affixes are elided in forming compounds. If the word स्त्री after its affix had been elided, still retained its old designation of Anga, the स्त्री + अर्थं would have been स्त्रियर्थं, the augment iyan being added by the rule already referred to above.,