Nyāya Sūtras 2.35

2.35

chalajātinigrahasthānānāṃ pṛthagupadeśa upalakṣaṇārtham iti/ upalakṣitānāṃ svavākye parivarjanam, chalajātinigrahasthānānāṃ paravākye paryanuyogaḥ/ jāteś ca pareṇa prayujyamānāyāḥ sulabhaḥ samādhiḥ, svayaṃ ca sukaraḥ prayoga iti/

The separate instruction of quibble, futile rejoinder, and points of defeat is for the sake of definition. [The purpose is] the avoidance in one's own speech of what has been defined, and the cross-examination of quibble, futile rejoinder, and points of defeat in an opponent's speech; and so that the resolution of a futile rejoinder employed by an opponent is easy to obtain, and its application by oneself is easy to make.