तव्यत्तव्यानीयरः

The affixes तव्यत् , तव्य and अनीयर् come after the verbal roots.
The phrase 'after verbal roots' is understood in this aphorism by anuvritti from sutra 91. The final letters त् of तव्यत् and र् of अनीयर् are for the sake of indicating accent, being merely diacritical letters. The letter त् indicating svarita accent (VI.I.I85) and the letter र indicating penultimate udatta accent 6.1.217; these being exceptions to the general rule of accent given in sutra 3 ante of this chapter.

Thus कृ + तव्यत् = कर्तव्यम्, and कृ + तव्य = कर्तव्यम् 'must be done'; कृ + अनीयर् = करणीयम् 'must be done'. In these cases the sense being that of the action itself, there is neuter gender singular number.

Vart:- The affix तव्यत् when coming after the verb वस् 'to dwell' in marking the agent, is treated as if it had an indicatory ण. The force of ण् is to cause vriddhi. Thus वस् + तव्यत् =वास्तव्यः 'a dweller'. Here the word is in the masculine gender, as the force of the affix is that of the agent, and not as it generally has that of an act or object 3.4.70.

Vart:- The affix केलिमर् should be enumerated in addition to those already enumerated in this aphorism. Thus पचेलिमा माषाः 'kidney beans fit to be
cooked'; भिदेलिमानि काष्ठानि 'the woods are apt to be split i. e: 'fragile'. This affix is to be employed when it is intended to express an object alone (i. e. in the passive and reflexive sense) and cannot be employed like those enumerated above, to denote also the action.