Nyāya Sūtras 2.20

2.20

tatra vādajalpau saprayojanau/ vitaṇḍā tu parīkṣyate/ vitaṇḍayā pravartamāno vaitaṇḍikaḥ/ sa prayojanam anuyukto yadi pratipadyate so 'sya pakṣaḥ so 'sya siddhānta iti, vaitaṇḍikatvaṃ jahāti/ atha na pratipadyate nāyaṃ laukiko na parīkṣaka ity āpadyate/ athāpi parapakṣapratiṣedhajñāpanaṃ prayojanaṃ bravīti, etad api tādṛg eva/ yo jñāpayati yo jānāti yena jñāpyate yac ca jñāpyate etac ca pratipadyate yadi, tadā vaitaṇḍikatvaṃ jahāti/ atha na pratipadyate, parapakṣapratiṣedhajñāpanaṃ prayojanam ity etad asya vākyam anarthakaṃ bhavati/ vākyasamūhaś ca sthāpanāhīno vitaṇḍā, tasya yady abhidheyaṃ pratipadyate, so 'sya pakṣaḥ sthāpanīyo bhavati/ atha na pratipadyate, pralāpamātram anarthakaṃ bhavati, vitaṇḍātvaṃ nivartata iti/
atha dṛṣṭāntaḥ pratyakṣaviṣayo 'rthaḥ, yatra laukikaparīkṣakāṇāṃ darśanaṃ na vyāhanyate/

Among these, philosophical debate and disputation have a purpose. Cavil, however, is examined [as follows]: a caviller is one who engages through cavil. If, when questioned about his purpose, he accepts that 'this is his thesis, this is his established tenet', he abandons being a caviller. If he does not accept it, the consequence follows that he is neither an ordinary person nor a critical investigator. If, alternatively, he says that his purpose is making known the refutation of the opponent's thesis, even this is just the same: if he accepts who makes it known, who knows, by what means it is made known, and what is made known, then he abandons being a caviller. If he does not accept it, his statement that 'the purpose is making known the refutation of the opponent's thesis' becomes meaningless. And a collection of statements devoid of proof is cavil; if he accepts what is expressed by it, that becomes his thesis that must be proven. If he does not accept it, it becomes mere meaningless babble, and its nature as cavil ceases.
Now, an example is an object within the realm of perception, regarding which the understanding of ordinary persons and critical investigators is not contradicted.