तुह्योस्तातङ्ङाशिष्यन्यतरस्याम्

तातङ् is optionally substituted for the affixes तु and हि of the Imperative, when Benediction is meant.
As जीवताद् भवान्, जीवतात् त्वम्, जीवतु भवान्, जीव त्वम् ॥ The ङ् prevents Guna and Vriddhi, 1.1.4, and the substitute replaces the whole affix (1.1.53 notwithstanding). The substitute is not sthanivat पित्, though it replaces a पित् affix, because it has its own indicatory letter ङ्, and ङित् does not become पित्; and consequently in ब्रूतात् ई is not added to the affix, by 7.3.93. ई being added only to पित् affixes after ब्रू ॥ When not denoting benediction, we have not this substitution : as ग्रामं गच्छतु भवान् or गच्छ ग्रामम् ॥

The affix तातङ् being a substitute of हि, is like हि, and, therefore, rules propounded with regard to हि, will apply to तातङ् also. Thus 6.4.105 says that after stems ending in short अ, the हि is elided: therefore, after such words तातङ् should also be elided. Therefore we cannot get the form जीवतात् त्वम् for जीवत्वम् ॥ This objection, however, is futile; for, in the sutra अतो हे (V1.4. 105), there is the anuvritti of हि from sutra 6.4.101 (हु झलभ्यो हेर्द्धिः) ॥ So that अतो हे should be construed as meaning "there is the elision of हि when it is of the form हि, and not when it assumes the form तातङ्" ॥

The object of ङ् in तातङ् is, as we have said above, for the sake of preventing Guna and Vriddhi. It should not be said that the object of ङ् in तातङ् is for the sake of अन्त्यविधिः by the application of sutra ङिच्च (1.1. 53), just as the substitutes अनङ् &c 7.1.93 and 7.1.94 apply to the finals. For by so doing, तातङ् would replace only the उ of तु and the इ of हि, which is not desired. And the case of तातङ् is to be distinguished from अनङ्, for in अनङ् the ङ् has no other object but to prevent sarvadesa; but in तातङ् we see that ङ् has another object, namely, the prevention of Guna and Vriddhi ; and ङ् having thus found scope, the तातङ् substitute will be governed by the general rule अनेकाल् शित् सर्वस्य 1.1.55.

The Karika given below raises these points.

Karika :-

तातङि ङित्त्वं संक्रमकृत्स्यादन्त्यविधिश्चेत्तच्च तथा न ।
हेरधिकारे हेरधिकारो लोपविधौ तु ज्ञापकमाह ॥
तातङो ङित्त्वसामर्थ्यान्नायमन्त्यविधिः स्मृतः ।
न तद्वदनङादीनां तेन तेऽन्त्यविकारजाः ॥

Karika:- In तातङ् the ङ् is for the sake of preventing Guna and Vriddhi (संक्रम = गुणवृद्धिप्रतिषेधः)॥ If it be said, it is for the sake of अन्त्यविधि by 1.1.53; we say it is not so. (If you say that after roots ending in short अ, तात् should be elided, by 6.4.105 read with 1.1.56, we reply): when the anuvritti or adhikara of हि was already existent in the sutra 6.4.105 from sutra 6.4.101, the express employment of हि in 6.4.105, indicates that the lopa rule does not apply to तातङ् ॥ (The lopa-rule not applying to तातङ्, it follows that it replaces the whole of हि and not only its final). The ङ् in तातङ् finds its scope in preventing Guna and Vriddhi, therefore, it is not for the sake of antya vidhi 1.1.53. The ङित्व in अनङ् &c has no other scope, therefore, these substitutes replace the final only.