अविज्ञाततत्त्वेऽर्थे कारणोपपत्तितस्तत्त्वज्ञानार्थमूहस्तर्कः ।
avijñāta-tattve’rthe kāraṇopapattitas tattva-jñānārtham ūhas tarkaḥ |
(Nyāya-sūtra: 1.1.40)
“Tarka is [a type of] deliberation in the form of demonstration [i.e., proposition] of causes for the purpose of [attaining] knowledge of the nature (tattva) of an object the nature of which is unknown.”